— An upswing in violence across southern Syria has prevented thousands of refugees from crossing into Jordan, according to U.N. officials, who are warning of an impending humanitarian crisis along the Jordanian-Syrian border.

According to the United Nations High Commissioner for Refugees, intensified clashes and shelling along the 230-mile-border has prevented thousands of Syrians from reaching Jordan since Saturday, shrinking a refugee influx which at one point averaged some 2,500 persons per day into the single digits.

“From what we are seeing right now, the violence has cut off all access routes to Jordan,” said Andrew Harper, UNHCR representative inside Jordan. “If thousands are continued to be displaced within Syria, we are very concerned that there is a large population stranded in southern Syria.”

On a day that the United States, Britain, France, Italy, Germany and regional powers met to discuss peace prospects in the so-called Friends of Syria gathering in the Jordanian capital, a single, injured Syrian made it across the border, relief officials said, following consecutive nights that saw nine, three and 13 new arrivals, respectively.

The drop-off comes as Damascus continues its month-long, sweeping military offensive across the southern region seen by observers as a bid to strengthen Bashar al-Assad’s regime’s hand ahead of potential peace talks in Geneva next month.

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According to Free Syrian Army officials, the campaign has seen Damascus retake several border towns such as Tal Shihab, Khirbet Ghazaleh and Sahem Al Golan — key rebel strongholds that served as hubs for displaced persons and key transit points on smuggling routes into Jordan.

“The regime is dropping more rockets on us in a day than it has in previous months,” said Mohammed al-Darawi, a Free Syrian Army battalion leader stationed outside the southern city of Daraa, which lies less than a mile from the Jordanian border. “Right now no one can move in southern Syria without the risk of getting hit.”

According to Darawi and residents of the border towns, some 10,000 displaced Syrians have massed along the border — a backlog they expect to double unless there is a break in hostilities.

The de-facto blockade has stoked fears among Syrians already living in Jordan, many of whom have called on their relatives in Syria to join them due to the rising violence and fears of retaliatory “massacres” in towns and villages recently retaken by regime forces.

Abu Malek al-Halibi said he has spent the past three days awaiting news of his wife and two children, who left from Aleppo for Jordan one week ago.

“The last I heard, they were heading to the town of Tal Shihab,” said the 54-year-old former police officer, who fled to the northern Jordanian city of Mafraq with his son six months ago. “Now only God knows if they have been taken by a missile or regime forces.”

The drop in refugee numbers has raised questions over Jordanian border policy, with some Syrian activists and media reports claiming that Jordanian military forces have begun turning away the thousands of refugees trying to enter the country each day.

Jordanian officials say Amman has not reversed the open-border policy that has resulted in the influx of over a half-million Syrians since March 2011. Forces are actively patrolling the mountainous border in search of Syrians who manage to break through the blockade, they say.

“We are ready to receive, treat and transfer refugees that make it to the Jordanian side of the border — but none are coming,” says Brig. Gen. Hussein Al Zayoud, head of the Jordanian border guard.

Harper and other UNHCR officials have called on Damascus to open southern Syria to aid agencies in order to ensure a supply of badly needed medical assistance and food aid to under-siege residents.

As violence continued to flare across southern Syria on Wednesday and talks continued over a still-elusive peace process, the fate of thousands such as Halibi’s family continued to hang in the balance.

“We no longer care about conferences, or transition governments or freedoms,” Halibi said. “All we want is to be with our families again.”