AMMAN, Jordan (AP) — Syrian opposition activists and witnesses said Tuesday that several thousand Syrians stranded on the border with Jordan have fled one makeshift camp for another, running from shelling and nearby fighting between Syrian rebels and government forces.

A Jordanian official confirmed that residents of Hadalat camp in the remote desert of southeastern Syria "were moved." He spoke on condition of anonymity because he was not authorized to discuss the issue with reporters.

Fighting in southwestern Syria ebbed in recent weeks, after a cease-fire deal brokered by the U.S., Russia and Jordan in July. At the same time, Syrian government troops have been advancing in the southeast, close to the borders with Jordan and Iraq.

Rami Abdurrahman, who heads the Britain-based Syrian Observatory for Human Rights, said Tuesday that civilians and armed rebels began leaving Hadalat at the beginning of September.

Syrian troops have been advancing in the southeast, "taking area after area," and Hadalat residents fled because government forces were getting closer, said Abdurrahman, whose group relies on a network of activists across Syria.

Hadalat had sheltered some 5,000 people, including relatives of rebels from two groups affiliated with the Free Syrian Army, a Western-backed coalition fighting to overthrow President Bashar Assad.

Rebel militias helped evacuate Hadalat's civilians, all of whom had fled by the end of last week, according to rebel officials and displaced residents.

Most civilians fled to the larger border camp of Rukban further to the east, with population estimates there ranging from the U.N's 45,000 to double that figure.

The number of displaced Syrians on Jordan's border had been rising since the kingdom began restricting entry in 2014. Residents of the tent camps on the border have endured severe hardships, including harsh weather and scarce food, water and medical aid.

Jordan closed the border formally in 2016, after an Islamic State car bomb launched from near Rukban killed seven Jordanian border guards.

Mohammed al-Adnan, a spokesman for the Tribal Army, a Jordan-backed Syrian militia, said Tuesday that all civilians had left Hadalat and that only some armed men remained there.

A Hadalat resident said that after shelling increased, he paid $400 to get his family of six on a truck out of the camp.

"We paid everything we had to get out," the 41-year-old said from Rukban.

"If the people here at the Jordanian border don't die from bombs, they will die from hunger and thirst," he said, referring to the dire conditions in isolated Rukban, which is now struggling to absorb several thousand more people.

Another displaced Hadalat resident said his family of eight doesn't even have a tent in Rukban. "We don't have any of the basics for living," said the 39-year-old.

Both displaced residents spoke on condition of anonymity for fear of repercussions from Syrian authorities.

The U.N. refugee agency's attempts to deliver aid to the border camps from Jordan have been disrupted frequently since the 2016 border closure.

The agency's Jordan office said Tuesday that it will keep trying to deliver aid, but did not say how this might work at a time when front lines in the area are shifting.

Mohammad Darbas al-Khalidi, a local leader in Rukban, said no aid has reached the camp for three months. He said he believes camp residents are unlikely to return to government-controlled areas of Syria, even if the situation in Rukban worsens.

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Associated Press writers Sarah El Deeb and Philip Issa in Beirut, and Karin Laub in Amman contributed to this report.