KABUL, Afghanistan — The Taliban have overrun a border district in the southeastern Afghan province of Paktia and inflicted heavy casualties on the Afghan security forces, officials said Saturday, as the insurgent fighters opened a new front in a once-volatile region.

Local officials expressed alarm that the attack in the Jani Khel district overnight Friday was led by fighters of the Haqqani network. The network, an arm of the insurgency based in Pakistan, is known for its urban assaults, and the officials say it is trying to create a foothold to re-establish its headquarters in Afghanistan.

Abdul Rahman Zurmati, Jani Khel’s governor, said his troops had been under siege for nine days. The district fell to the Taliban late Friday, he said, because his forces ran out of ammunition and reinforcements did not arrive.

“We were 90 people, and we had to fight against 1,200 Taliban,” Mr. Zurmati said in a phone interview. “Twenty-seven of my men have been killed. At first, some of them were wounded and we brought them to the main road, but then a land mine exploded and they were killed. We killed 130 of the enemy.”