Russian President Vladimir Putin called for international recognition of Crimea as part of Russia, an end to Ukraine's Nato membership bid and a halt to weapons shipments there.
Putin claimed that Russia's 2014 annexation of Ukraine's Crimean Peninsula should be internationally recognised as a legitimate reflection of the local population's choice, likening it to a vote for Kosovo independence.
The annexation has been widely condemned by Western powers as a breach of international law.
To end the current crisis, he also called for the renunciation of Ukraine's Nato bid, saying it should assume a "neutral status", and said that the West should stop sending weapons there.
Earlier, Russian lawmakers gave President Vladimir Putin permission to use military force outside the country — a move that could presage a broader attack on Ukraine after the US said an invasion was already under way there.
In a fresh development, Russia says it is evacuating the country's diplomatic personnel from Ukraine because they received threats.
Several European leaders said Russian troops have moved into rebel-held areas in eastern Ukraine after Putin recognised their independence. But it was unclear how large the movements were, and Ukraine and its Western allies have said Russian troops have been fighting in the region since the separatist conflict erupted in 2014. Moscow denies those allegations.
Members of the upper house, the Federation Council, voted unanimously to allow Putin to use military force outside Russia — effectively formalising a Russian military deployment to the rebel regions, where an eight-year conflict has killed nearly 14,000 people.
The White House on Tuesday began referring to Russian troop deployments in eastern Ukraine as an "invasion" after initially hesitating to use the term — a red line that President Joe Biden has said would result in the US levying severe sanctions against Moscow.
"We think this is, yes, the beginning of an invasion, Russia's latest invasion into Ukraine," said Jon Finer, principal deputy national security adviser, in an interview on CNN. "An invasion is an invasion and that is what is under way."
The administration resisted initially calling the deployment of troops an invasion because the White House wanted to see what Russia was actually going to do. After assessing Russian troop movements, it became clear it was a new invasion, the official added.
White House press secretary Jen Psaki also alluded to the Russian action as an invasion in a Twitter post commenting on Germany chancellor Olaf Scholz's decision to halt the Nord Stream 2 gas pipeline in response to Russia's actions.
The US president "made clear that if Russia invaded Ukraine, we would act with Germany to ensure Nord Stream 2 does not move forward," Psaki said.
For weeks, Western powers have been bracing for an invasion as Russia massed an estimated 150,000 troops on three sides of neighbouring Ukraine. They warned an attack would cause massive casualties, energy shortages in Europe, and economic chaos around the globe — and promised swift and severe sanctions if it materialised. The European Union and Britain announced Tuesday that some of those measures were coming.
Western leaders have long warned Moscow would look for cover to invade — and just such a pretext appeared to come on Monday when Putin recognised as independent two separatist regions in eastern Ukraine, where Government troops have fought Russia-backed rebels in a conflict that has killed over 14,000 people.
The Kremlin then raised the stakes further Tuesday, by saying that recognition extends even to the large parts now held by Ukrainian forces.
Kremlin spokesman Dmitry Peskov said that Russia has recognised the rebel regions' independence "in borders that existed when they proclaimed" their independence in 2014 — broad territories that extend far beyond the areas now under the rebel control and that include the major Azov Sea port of Mariupol.
Putin's move to recognise the territories' independence opened the door for him to formalise his hold on them and send forces in, though Ukraine and its Western allies have charged Russian troops have been fighting there for years. Moscow denies those allegations.
Condemnation from around the world was quick. Ukrainian President Volodymyr Zelenskyy said he would consider breaking diplomatic ties with Russia and Kyiv recalled its ambassador in Moscow.
But confusion over what exactly was happening in eastern Ukraine threatened to hobble a Western response. While the US clearly called it an invasion, other allies hedged.
"Russian troops have entered in Donbas," the name for the area where the two separatist regions are located, EU foreign policy chief Josep Borrell said in Paris. "We consider Donbas part of Ukraine."
But in a distinction that could complicate a European and Western response, he added: "I wouldn't say that [it is] a fully fledged invasion, but Russian troops are on Ukrainian soil."
Poland's Defence Ministry and British Health Secretary Sajid Javid also said Russian forces had entered Ukraine's east, with Javid telling Sky News that "the invasion of Ukraine has begun".
Spanish Foreign Minister Jose Manuel Albares noted "if Russia uses force against Ukraine, sanctions will be massive".
The Kremlin hasn't confirmed any troop deployments to the rebel east, saying it will depend on the security situation. Vladislav Brig, a member of the separatist local council in Donetsk, told reporters that the Russian troops already had moved in, but more senior rebel leaders didn't confirm that.
Late Monday, convoys of armoured vehicles were seen rolling across the separatist-controlled territories. It wasn't immediately clear if they were Russian.
In response to the moves thus far, top EU officials said the bloc was prepared to impose sanctions on several Russian officials and banks financing the Russian armed forces and move to limit Moscow's access to EU capital and financial markets. They gave few details.
EU foreign ministers are meeting later Tuesday to discuss the measures — but they did not appear to include the massive punishment repeatedly promised in case of a full-fledged invasion.
British Prime Minister Boris Johnson also said the UK would slap sanctions on five Russian banks and three wealthy individuals.
While he said that Russian tanks have already rolled into eastern Ukraine, he warned a full-scale offensive would bring "further powerful sanctions".
The White House has also moved to respond, issuing an executive order to prohibit US investment and trade in the separatist regions, and additional measures — likely sanctions — were to be announced Tuesday. Those sanctions are independent of what Washington has prepared in the event of a Russian invasion, according to a senior administration official who briefed reporters on the condition of anonymity.
The Russian moves also pushed Germany to suspend the certification process for Nord Stream 2 pipeline that was to bring natural gas from Russia. The pipeline was built to help Germany meet its energy needs, particularly as it switches off its last three nuclear power plants and phases out the use of coal. It has resisted calls by the US and others to halt the project.
As world leaders scrambled to decide on their response, legislation that will likely set the stage for a deeper move into Ukrainian territory moved through Russia's parliament.
The bills, which sailed quickly through the Kremlin-controlled parliament, envisage military ties between Moscow and the separatist regions, including possible deployment of Russian military bases in the separatist regions.
Even as alarm spread across the globe, Zelenskyy, the Ukrainian president, sought to project calm, telling the country in an address overnight: "We are not afraid of anyone or anything. We don't owe anyone anything. And we won't give anything to anyone."
His foreign minister, Dmytro Kuleba, will be in Washington on Tuesday to meet Secretary of State Antony Blinken, the State Department said.
Russia has long denied it has any plans to invade Ukraine, instead blaming the US and its allies for the current crisis and describing Ukraine's bid to join Nato as an existential challenge to Russia. Putin reiterated those accusations in an hour-long televised speech on Monday, when he announced that Russia would recognise the rebels.
"Ukraine's membership in Nato poses a direct threat to Russia's security," he said.
Russia says it wants Western guarantees that Nato won't allow Ukraine and other former Soviet countries to join as members. Moscow has also demanded the alliance halt weapons deployments to Ukraine and roll back its forces from Eastern Europe — demands flatly rejected by the West.
Putin warned Monday that the Western rejection of Moscow's demands gives Russia the right to take other steps to protect its security.