Libyan rebels seized control of a remote border crossing with Tunisia on Thursday, witnesses said, after a week of intense fighting in the western mountains that has caused thousands to flee.

The Tunisian state news agency TAP reported that 13 Libyan officers and soldiers, including a general, handed themselves over to the Tunisian military at the border. They apparently sought refuge after the clashes with opposition fighters. Rebels and witnesses told news agencies that the Libyan side of the border at Dehiba was in rebel hands.

Later, the Libyan government said it had sent more troops to the area and reclaimed control of the border post, but this could not be independently verified. “Now it’s calm and under control of our military,” Deputy Foreign Minister Khaled Kaim told reporters early Friday.

A renewed government assault on the Nafusa mountains has sent about 14,000 men, women and children, most of them ethnic Berbers, fleeing from a largely overlooked theater of the conflict, according to the Office of the United Nations High Commissioner for Refugees (UNHCR).

Berbers have long faced suspicion and discrimination under Libyan leader Moammar Gaddafi’s rule, and many towns and villages took part in the uprising against him that began in mid-February. In recent days, the government has made a renewed bid to reclaim the Nafusa mountains, which begin about 60 miles south of Tripoli and stretch westward to the Tunisian border, from rebel control.

With foreign journalists unable to travel to the region, information is difficult to corroborate, and the area has received little media attention.

Moussa Ibrahim, a spokesman for the Libyan government, said rebels had deliberately driven people out of mountain villages and into Tunisia “to create a humanitarian disaster area, to encourage NATO to come in.”

“We had intelligence that they were planning this,” he said. “We believe [the refugees] have been taken there against their will. We consider them to be hostages.”

But refugees blamed the government, saying that their homes had been searched and often burned, that tanks had been turned on their villages and that their livestock had been killed.

“We fled because we can’t face heavy weapons,” 33-year-old Sefao, a refu­gee from the village of Yafran, which has a population of about 25,000, said by telephone from a camp in Tunisia. He asked for his full name to be withheld to protect family members still inside Libya. “There are tanks inside Yafran. They are killing everywhere.”

Families have fled in cars loaded with mattresses and blankets, traveling on back roads and avoiding official border crossings staffed by Gaddafi loyalists.

“The whole of the western mountains has been under siege for about a month now,” said Firas Kayal of the UNHCR. He said refugees told him that they had fled because of intensified fighting between both sides, because government troops were advancing and because of shelling and rocket attacks by Gaddafi’s forces.

A rebel fighter, who gave his name as Belgassem, told the Associated Press that since the weekend, Yafran has come under daily attack with Russian-made truck-mounted Grad rockets, tank shells and antiaircraft guns. A water tank and houses in the village had been damaged and the hospital evacuated, he said.

“According to witness accounts I heard in the refugee camp, dozens of people — civilians and rebels — were killed over the last seven days,” a Libyan doctor who gave his name as Abdelrahman told Reuters on Wednesday from a Tunisian refugee camp in Dehiba. “Most were killed in the last three days, when the attacks intensified.”

Gaddafi called Berbers, also known as Amazigh, a “product of colonialism” created by the West to divide Libya. The Berber language was not recognized or taught in schools, and it was forbidden in Libya to give children Berber names.

The policy was eased in 2007, but a U.S. Embassy cable released by WikiLeaks said this relaxation was limited and quoted Gaddafi as telling community leaders: “You can call yourselves whatever you want inside your homes — Berbers, Children of Satan, whatever — but you are only Libyans when you leave your homes.”

Sefao, the refu­gee, said the government had arrested many ethnic Berbers since the uprising began, including his cousin, who was detained by security forces when he went to the nearby garrison town of Gharyan to try to buy fuel. “He supported the revolution, but in a peaceful way,” Sefao said.

Amnesty International said it had come across many such accounts of disappearances. “Since, there has been no news of the fate or whereabouts of many of them,” Diana Eltahawy, Libya researcher at Amnesty International, said in a report. “Others, however, have been shown on Libyan state television ‘confessing’ to having been pressured to act against Libya’s ‘best interest.’ ”

Ibrahim, the government spokesman, said the army controlled “the urban centers” in the mountain region. “The rebels in the western mountains are weak; their numbers are not more than a few hundred,” he said, adding that they were holding out only because of the rough mountain terrain and because they were sheltering in caves.

But rebels said most towns and villages in the mountains were “liberated” from Gaddafi’s control.