An al-Qaeda-inspired group says it will march on Baghdad after seizing two key Sunni cities in Iraq.
The UN Security Council has deplored the terrorist attack in Iraq's second-largest city of Mosul "in the strongest terms" and is demanding the immediate return of all hostages abducted from the Turkish consulate.
It also condemned recent terrorist attacks elsewhere in Iraq aimed at destabilising the country and region.
The council reaffirmed its support for the Iraqi people and government and reiterated that "no act of violence or terrorism can reverse a path towards peace, democracy and reconstruction in Iraq".
The press statement backed the government's plans for a national unity meeting to combat terrorist threats.
The UN envoy in Iraq is scheduled to brief the council at a closed meeting Thursday (local time).
Iraq foreign minister: Iraq faces 'mortal threat'
The fall of the major northern Iraqi city of Mosul to insurgents must push the country's leaders to work together and deal with the "mortal threat" facing Iraq, the country's foreign minister said.
Speaking on the sidelines of an Athens meeting of European Union and Arab League foreign ministers, Hoshyar Zebari said he had assured his colleagues there would be "closer cooperation" between Baghdad and the Kurdistan regional government to push the insurgents out of Mosul.
Most of the city was seized Tuesday (local time) in a major assault by al-Qaeda-inspired militants known as the Islamic State of Iraq and the Levant, who took control of government buildings and pushed out security forces as thousands of residents fled.
Zebari said it was "dramatic" for a large city like Mosul to fall and the security forces to be overrun, but added he was confident Iraqi security forces, along with Kurdish forces, would be able to push back the insurgents.
Speaking to a small number of reporters, he said he had assured his colleagues that there "would be a closer cooperation between Baghdad and the Kurdistan regional government to work together and try to flush out these foreign fighters".
Zebari, who is from Mosul himself, said there was no time to waste.
"You cannot leave these people to stay there, to entrench themselves for a long time. So there has to be really a quick response to what has happened," he said.
The foreign minister said he hoped the incident would "lead all the Iraqi leaders to come together to face this serious, mortal threat to the country."
"It could be an inducement to all of them to think about the greater interest and to resolve the problems and to form a new government on the basis of a national unity government," he said.
The EU and Arab League foreign ministers issued a joint statement condemning "in the strongest terms the recent wave of terrorist attacks" and calling on the Iraqi and the Kurdistan regional governments "to combine their political and military forces in order to restore security".
Speaking at the end of the one-day meeting, Belgian Foreign Minister Didier Reynders described the situation in Iraq as "very dangerous," adding that "we obviously want to maintain the integrity of the territory, the unity of the country, and it's particularly worrying to see a part of the country fall under the control of extremist groups once again".