BEIRUT/AMMAN (Reuters) - A ceasefire has been agreed for southern Syria between the government and rebels, a Jordanian official source said on Friday, amid fears of a gathering humanitarian catastrophe in a region sensitive to neighbors Jordan and Israel.

Residents celebrate the army's arrival in the formerly rebel-held town of Ibta, northeast of Deraa city, Syria in this handout released on June 29, 2018. SANA/Handout via REUTERS

In Washington, a State Department official said the United Sattes could not confirm the truce report, and the situation in southern Syria remained “grim” with Russia and Syrian government forces continuing to bomb the area.

Lebanon’s Iran-backed Hezbollah, which fights alongside Damascus, said meanwhile that a “very big victory” was near in southern Syria, where pro-government forces have made rapid gains in Deraa province.

State media said troops had marched into several towns and a rebel official said opposition front lines had collapsed.

Government forces backed by Russian air power have turned their focus to the southwest since defeating the last remaining besieged insurgent pockets including eastern Ghouta, near Damascus.

A war monitoring group said the offensive has uprooted more than 120,000 civilians in the southwest since it began last week. Tens of thousands of people have fled toward the border with Jordan and thousands more to the frontier with the Israeli-occupied Golan Heights.

The U.N. refugee agency said the number of displaced people in southern Syria had more than tripled to 160,000 in the latest fighting.

Israel and Jordan -- which already hosts over 666,000 U.N. registered refugees -- say they will not let refugees in.

“We left under bombardment, barrel bombs, (air strikes by) Russian and Syrian warplanes,” said Abu Khaled al-Hariri, 36, who fled from al-Harak town to the Golan frontier with his wife and five children.

“We are waiting for God to help us, for tents, blankets, mattresses, aid for our children to eat and drink.”

President Bashar al-Assad has pressed ahead with the offensive despite U.S. warnings of “serious repercussions”. Washington has told rebels not to expect military support against the assault.

The campaign has shattered a “de-escalation” deal negotiated by the United States, Russia and Jordan that had mostly contained fighting in the southwest since last year.

A Jordanian official source told Reuters there were confirmed reports of a ceasefire in southern Syria that would lead to “reconciliation” between opposition and government forces. The source did not elaborate.

Jordan has been facilitating talks between rebel factions and Moscow over a deal that would end the violence in return for the return state rule to Deraa province.

U.N. High Commissioner for Human Rights Zeid Ra’ad al-Hussein warned that many civilians risk being trapped between government forces, rebels, and Islamic State which has a small foothold there - an outcome he said would be a “catastrophe”.

“The real concern is that we are going to see a repetition of what we saw in eastern Ghouta - the bloodshed, the suffering, the civilians being held, being under a siege,” U.N. human rights spokeswoman Liz Throssell said.

The Syrian Observatory for Human Rights, a UK-based war monitoring group, said the campaign had killed at least 98 civilians since June 19.

Slideshow ( 11 images )

The chief Syrian opposition negotiator Nasr al-Hariri has decried “U.S. silence” over the offensive and said only a “malicious deal” could explain the lack of a U.S. response.

The Kremlin said Russian President Vladimir Putin and U.S. President Donald Trump will have a detailed discussion about Syria when they meet in July.

EASTERN DERAA PROVINCE

The war has been going Assad’s way since Russia intervened on his side in 2015, when he held just a fraction of the country. Today he commands the single largest part of Syria, though much of the north and east is outside his control.

Syrian troops have seized a swathe of rebel territory northeast of Deraa city. State TV broadcast scenes of what they said were locals celebrating the army’s arrival in the formerly rebel-held town of Ibta and said rebels turned in their weapons.

The assault has so far targeted Deraa, not rebel-held parts of nearby Quneitra province at the Golan which are more sensitive to Israel.

State media said that government forces seized al-Harak and Rakham towns, and that insurgents in four other towns agreed to surrender their arms and make “reconciliation” deals.

A series of offensives and local deals - accept state rule or leave - has helped Damascus suppress insurgent bastions across western Syria.

“Most of the (people in) the eastern villages have fled to west Deraa and to Quneitra,” said Abu Shaima, a Free Syrian Army rebel spokesman. Another rebel official said some towns were trying to negotiate deals with the state on their own. “There was a collapse in the eastern front yesterday,” he added. “The front in Deraa city is steadfast.”

ISRAEL SENDS AID, WON’T OPEN FRONTIER

Observatory Director Rami Abdulrahman, speaking by phone, said some people had also fled to government territory, while others crossed to a corner of southwest Syria held by an Islamic State-affiliated group.

Jordan reiterated its position that newly displaced Syrians must be helped inside Syria. “Jordan has reached its capacity in receiving refugees,” Foreign Minister Ayman Safadi told the pan-Arab broadcaster al-Jazeera late on Thursday.

Israeli Energy Minister Yuval Steinitz, in an interview with Tel Aviv Radio 102FM, said: “I think we must prevent the entry of refugees from Syria to Israel, in the past we have prevented such cases.”

The Israeli military said an increased number of civilians had been spotted in refugee camps on the Syrian side of the Golan over the past few days, and that it had overnight sent aid supplies at four locations to people fleeing hostilities.