Syria's neighbours are increasingly being drawn into the country's civil war in a variety of ways, whether militarily or due to an exodus of Syrians fleeing the fighting at home.
The spillover has raised concerns that the nearly 20-month-long conflict between Syrian President Bashar Assad's regime and rebels trying to topple him could endanger the entire Middle East.
Here is a look at how neighbouring states are being affected by Syria's bloodletting:
Turkey has struck the Syrian military repeatedly in response to shelling and mortar rounds from Syria since October 3, when shells from Syria struck the Turkish village of Akcakale, killing two women and three children. The incident prompted NATO to convene an emergency meeting and Turkey sent tanks and anti-aircraft batteries to the area. Turkey's military has also scrambled fighter jets after Syrian helicopters flew close to the border.
There are about 120,000 Syrian refugees sheltering in Turkish camps, with up to 70,000 more living in Turkey outside the camps. Thousands more wait at the border, held up as Turkey struggles to cope with the influx.
Turkey also hosts much of the opposition and rebel leadership.
Turkey has called for a buffer zone in Syria where the opposition and civilians would be protected, a step that would likely require international enforcement of a no-fly zone. Russia and China have blocked robust moves against the Syrian regime at the UN Security Council, and the United States has been reluctant to use its military in another Mideast conflict.
Israel has become the second country to strike the Syrian military, after Turkey. An Israeli tank hit a Syrian armoured vehicle after shells from fighting in Syria exploded in Israel-controlled Golan Heights. A day earlier, Israel fired a warning shot near a group of Syrian fighters.
Syrian shells have exploded inside the Golan several times in recent weeks damaging apple orchards, sparking fires and spreading panic but causing no injuries. In early November, three Syrian tanks entered the Golan demilitarised zone, and in a separate incident an Israeli patrol vehicle was peppered with bullets fired from Syria; no one was hurt in the incident and the Israeli military deemed it accidental.
There is concern in Israel that Assad may try to spark a conflict with Israel, opening up the potential for attacks by Lebanon's militant Hezbollah and Hamas in the Gaza Strip. Israel has also warned that Syria's chemical weapons could be turned on the Jewish state. Still, while no friend of Assad, Israel is also worried that if he is toppled, Syria could fall into the hands of Islamic extremists or descend into sectarian warfare.
Mortars and shells from the Syrian side regularly crash in Lebanon, causing several casualties, though Lebanese forces have never fired back. More dangerously, Syria's conflict has heightened deep rivalries and sectarian tensions in its smaller neighbour. Lebanon is divided between pro-Assad and anti-Assad factions, a legacy of the nearly three decades when Damascus all but ruled Lebanon, until 2005. Assad's ally, the Hezbollah militia is Lebanon's strongest political and military movement.
On October 19, a car bomb assassinated Lebanon's top intelligence chief, Wissam al-Hassan. Many in Lebanon blamed Syria and Hezbollah for the assassination.
The northern Lebanese city of Tripoli has seen repeated clashes between Sunni Muslims and Alawites - the Shiite offshoot sect to which Assad belongs. Battles in the city in May and August killed at least 23 people total and wounded dozens.
The kidnapping of Lebanese Shiites in Syria by rebels has also had repercussions in Lebanon. In May, Shiites blocked roads and burned tires in protest over the abductions, and later in the summer a powerful Shiite clan took 20 Syrians and a Turk in Lebanon captive in retaliation, all of whom have since been released.
Lebanon also shelters about 100,000 Syrian refugees.
Jordan has taken the brunt of the refugee exodus from Syria, with some 265,000 Syrians fleeing across the border. Around 42,000 of them are housed at Zaatari, a dust-filled refugee camp, where riots have broken out several times by Syrians angry over lack of services.
A growing number of stray Syrian missiles have fallen on Jordanian villages in the north in recent weeks, wounding several civilians.
Late last month, a Jordanian border patrol officer was killed in clashes with eight militants trying to cross into Syria. Hours earlier, Jordan announced the arrest of 11 suspected al-Qaeda-linked militants allegedly planning to attack shopping malls and Western diplomatic missions in Jordan.
Sunni and Shiite fighters from Iraq have made their way to Syria to join the civil war - the former on the side of the opposition, the latter siding with Assad's regime, according to Iraqi officials and Shiite militants. Sunni al-Qaeda fighters are believed to be moving between Iraq and Syria, and some al-Qaeda fighters in Iraq's western Anbar province have regrouped under the name of the Free Iraqi Army, a nod to the rebels' Free Syrian Army, Iraqi officials say.
The United States has pressured Baghdad to stop Iranian planes suspected of ferrying arms to Syria from using Iraqi airspace. Iraq has so far acknowledged only forcing two planes to land for inspection and said it didn't find any weapons either time.
About 49,000 Syrian refugees have temporarily resettled in Iraq, according to the UN refugee agency.