Government forces in south Syria are advancing along the frontier with Jordan and will soon reach a border crossing in rebel hands, a pro-Damascus commander said on Friday.

Several witnesses along the Jordan border fence with Syria said they spotted armored vehicles and a tank with a Russian flag heading toward the Nasib crossing.

A war monitor said troops in Deraa province reached the frontier on Thursday for the first time since 2015, part of a major offensive to recover the entire southwest from insurgents.

The commander in the regional alliance that backs Damascus told Reuters that the army and allies had arrived after seizing a string of villages. "Within a short period of time, they will reach the (Nassib) crossing," the non-Syrian commander said, speaking on condition of anonymity.

With the help of Russian air power, the assault has swept into Deraa’s insurgent territory in the past two weeks, shrinking one of the last rebel strongholds left across Syria.

The UN refugee agency has urged Jordan to open its borders as Syrians fleeing their homes en masse, seeking shelter from the battles and heavy air strikes. It says the fighting has uprooted more than 320,000 people, with 60,000 gathered at the Jordan border crossing and thousands more at the frontier with the Israeli-occupied Golan heights.

The Norwegian Refugee Council called it the largest displacement since the start of Syria’s seven-year war.

The Syrian Observatory for Human Rights said government forces were now around three km (two miles) away from the Nasib border crossing with Jordan.

The UK-based war monitoring group said an armed group which held some border villages had handed over control to the advancing troops without resistance.

A military media unit run by Lebanon’s Hezbollah, which fights alongside Damascus, said the army captured eight border outposts on Friday.

Hezbollah is helping lead the offensive but keeping a low profile, pro-Damascus sources have told Reuters, defying neighboring Israel’s demands that Iran-backed forces stay away from its frontier.

Jordan said on Thursday it had managed to convince the Syrian opposition and the Russians to meet again for talks over a deal to end the fighting.