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-Qaida-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-Qaida fighters are believed to be moving between Iraq and Syria, and some al-Qaida 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 U.N. refugee agency.