Hundreds of fighters from Iran-backed Iraqi militias crossed into Syria overnight to help the government fight rebels who seized Aleppo last week, Syrian and Iraqi sources said on Monday, and Tehran pledged to aid the Damascus government.

Approximately 200 Iraqi militiamen crossed into Syria overnight through the strategic Bou Kamal border crossing, according to an opposition war monitor.

Iran-backed militias from Iraq entered the country to support the government's attempts to contain surprise advances by the insurgents. Iran's foreign minister says the country stands by Syrian leader Bashar Assad.

Iranian-backed Iraqi militias have deployed in Syria to back the government’s counteroffensive against a surprise advance by insurgents who seized the largest city of Aleppo

Insurgents broke through government defense lines in Aleppo on Friday and entered the city’s western neighborhood with little resistance.

Iran, a key ally of President Bashar Assad, has pledged to help the government counter the surprise offensive.

The Syrian military has rushed in reinforcements to push back insurgents from advancing farther into the northern Hama countryside after they seized Aleppo in a surprise offensive

Syrian rebels launched a surprise attack on Saturday and quickly advanced through several provinces in the north and northwest of Syria, including the city of Aleppo, the country’s second largest city.