BAGHDAD/BEIRUT: Iraq’s mostly Iran-backed Shiite paramilitary forces reached the border with Syria Monday after securing a string of small villages west of Mosul, according to a spokesman for the group. The move follows a push by the government-sanctioned forces to retake a number of small villages and key supply lines from Daesh (ISIS) in the vast deserts west of Mosul. Iraq’s conventional military has focused on clearing the city itself, a slow, grinding process in dense urban terrain packed with tens of thousands of civilians.

The paramilitary forces – mostly Shiite fighters with close ties to Iran referred to as the Popular Mobilization – began Monday’s operation by pushing Daesh militants out of the center of the town of Baaj, some 40 km from the Syrian border, according to Shiite lawmaker Karim al-Nouri.

The fighters plan to “erect a dirt barricade and dig a trench” along the border, said Sheikh Sami al-Masoudi, a Popular Mobilization leader, describing how the forces would secure the porous border area that has long been a haven for smugglers and insurgent activity.

Masoudi described Baaj as the last Daesh supply line between Syria and Iraq in the area and said the paramilitary forces reached the border by retaking the village of Umm Jrais.

Iraq’s army, federal police and special forces launched the operation to retake Mosul last October with close backing from the U.S.-led international coalition. The city’s eastern half was declared liberated in January, and the push for the city’s western section, separated from the east by the Tigris River, began the following month.

Meanwhile, Popular Mobilization forces has largely operated in the desert to the west of Mosul, retaking small villages and cutting Daesh supply lines since October.

After securing the border area, Iraq’s Popular Mobilization forces are ready to move inside Syrian territories, according to Hashim al-Mousawi, a leader with the powerful Al-Nujaba militia, a part of the alliance.

But Mousawi added such a move would require the approval of the Iraqi government.

On the Syrian side of the border, U.S.-backed Syrian Democratic Forces, Daesh militants and Syrian rebels are fighting for territory. President Bashar Assad’s forces and their allies have also been on the offensive, moving toward the Iraqi and Jordanian border but are still far from reaching it.

On May 18, a U.S. airstrike hit pro-Syrian government forces that the U.S.-led coalition said posed a threat to American troops and allied rebels operating near the border with Jordan. The attack was the first such close confrontation between America troops and fighters backing Assad.

Syrian activists said leaflets were dropped Sunday on advancing Syrian soldiers and their allies, warning them to stay away from the border crossing of Tanf. “Any movements toward Tanf will be considered hostile and we will defend our forces,” the coalition leaflet read.

Monday, More airstrikes and artillery shelling hit Raqqa, the de facto capital of Daesh, activists said.

Airstrikes have intensified over the past days as U.S.-backed SDF fighters have pushed on toward the stronghold, now nearly surrounding it from the north, west and east. The extremists still have an exit from the south, even though the U.S.-led coalition destroyed two bridges on the Euphrates River south of Raqqa.

The Britain-based Syrian Observatory for Human Rights said the city was pounded by warplanes and artillery since early morning. The activist group had no immediate word on casualties from the new airstrikes, adding that about 38 people have been killed in Raqqa and its suburbs over the past three days. The activist-operated Raqqa is Being Slaughtered Silently said that since Sunday, the U.S.-led coalition carried out more than 30 airstrikes on the city, killing 35 people and destroying a school on Raqqa’s northern outskirts.

Sunday, opposition activists said the coalition dropped leaflets in Arabic on Raqqa, urging residents to leave the city.

Some leaflets gave instructions of how to leave Raqqa, calling on people to keep their plans secret from Daesh and to leave without any weapons and waiving a white banner.

“This is your last chance. Failing to leave could lead to death. Raqqa will fall. Don’t be there when it happens,” one of the leaflets read.

Daesh has been preventing people from leaving Raqqa and many fear that residents will be used as human shields when SDF, the most effective force fighting the extremists in Syria, begin marching in the city that has been held by Daesh since January 2014.