Iraq sent hundreds of Iran-backed fighters to Syria to help the Assad regime fight anti-regime forces who captured Aleppo last week.
At least 300 fighters, primarily from the Badr and Nujabaa groups, crossed late on Sunday using a dirt road to avoid the official border crossing, two Iraqi security sources said, adding that they were there to defend a Shi'ite shrine.
A senior Syrian military source said the fighters had crossed in small groups to avoid airstrikes. "These are fresh reinforcements being sent to aid our comrades on the front lines in the north," the source said.
The head of Iraq's Popular Mobilization Forces (Hashd al-Shaabi in Arabic) said no group under its umbrella had entered Syria, and that it does not operate outside Iraq.
Iran's constellation of allied regional militia groups has long been integral to the success of pro-regime forces in subduing the opposition who rose up against President Bashar Assad in 2011, and they have long maintained bases in Syria.
Iranian Foreign Minister Abbas Araqchi said on Monday that Syria's military was capable of confronting the opposition but, referring to the regional militia groups Tehran backs, he added that "resistance groups will help and Iran will provide any support needed."
The Syrian government and Russian warplanes intensified attacks on Monday in areas held by anti-regime forces in the northwest, residents and rescue workers said, including a strike on a displaced people's camp that killed seven.
The lightning anti-regime assault last week dealt Assad his biggest blow in years, reigniting a conflict that had appeared frozen for years after civil war front lines stabilized in 2020.
Russia, though focused on its war in Ukraine since 2022, retains an air base in northern Syria. The main Iran-backed group, Lebanon's Hezbollah, has been focused on its own war with Israel since the Gaza conflict began last year.
The United States and United Arab Emirates have discussed the possibility of trying to peel Assad away from Iran by offering to lift sanctions if he cuts off weapons routes to Lebanon's Hezbollah, sources familiar with the matter said.
The discussions took place before the opposition advance on Aleppo last week, the sources said.
Syria's conflict erupted in a rebellion against Assad's rule in 2011 and the opposition held much of Aleppo from 2012 until 2016, when government forces retook it with help from Russia and Iran-backed militia in a turning point of the war.
Any prolonged escalation in Syria risks further destabilizing a region roiled by the conflicts in Gaza and Lebanon, with millions of Syrians already displaced and with regional and global powers backing rival forces in the country.
The Turkish and Iranian foreign ministers discussed the fighting in Syria on Monday. Foreign Minister Hakan Fidan said opposition advances could not be explained by foreign intervention and urged the Syrian opposition to compromise.
A spokesperson for Israel's military said it would not let Iran exploit the Syria conflict to transfer weapons to Hezbollah.
Russia, whose 2015 entry into the conflict turned the military balance decisively in Assad's favor, continues to support him and is analyzing the situation on the ground, the Kremlin said.
On Sunday Moscow dismissed the general in charge of its forces in Syria, Russian war bloggers reported.
The Syrian government said Syrian and Russian air forces were striking opposition-held positions in the countryside east of Aleppo city.
The White Helmets rescue organization and residents of opposition-held areas in the north said warplanes had hit residential areas of Aleppo city and a displaced people's camp in Idlib province where seven people were killed, including five children.
The government said the military was working to secure a string of towns recaptured from anti-regime forces on Sunday that run along the front line north of Hama, between Aleppo and Damascus.
In Türkiye, Syrian opposition leader Hadi al-Bahra said the opposition sought to force Syria's government to accept a political transition. "We are ready to start negotiating tomorrow," Bahra said.
Anadolu Agency said the Türkiye-backed Syrian National Army (SNA) had taken the town of Tal Rifaat from the terrorist PKK's Syrian offshoot YPG and was advancing in outer areas of the district.
Opposition sources and an Aleppo resident said the YPG terrorist group was pulling out of the city's Sheikh Maqsoud district under a deal with opposition forces. The YPG had long held Sheikh Maqsoud.