KABUL, Afghanistan - Insurgents firing heavy machine guns, rocket-propelled grenades, and assault rifles killed 35 workers and guards in an attack on a NATO-funded road-construction site in a remote area of eastern Afghanistan, authorities said Thursday.

More than 100 fighters carried out the assault in Wazei Zadran in a mountainous region of Paktia province near neighboring Pakistan's lawless tribal areas, said the Galaxy Sky construction company owner, Noorullah Bidar. He described the assailants as Taliban fighters, though there was no immediate claim of responsibility.

The region is thought to be controlled largely by the Haqqani network, a fiercely independent branch of the Afghan Taliban and a major enemy of NATO forces. The al-Qaeda-affiliated network, led by ailing Jalaluddin Haqqani and his son Sirajuddin, is based in Pakistan's tribal belt.

U.S. officials say that Pakistan has not done enough to go after insurgent safe havens in the area, especially in North Waziristan, where the Haqqanis are thought to be based. The issue is a sore point between the two countries and the area has been the target of repeated U.S. drone strikes.

About 85 people were at the construction site at the time of the attack, including about 65 guards recruited from surrounding villages, Bidar said. He said that the firefight lasted about two hours and that the insurgents shot down at the camp from a nearby hill. The fighting also destroyed a number of construction vehicles.

"This was a brutal attack," Bidar said.

Rohullah Samon, spokesman for Gov. Juma Khan Hamard, said 35 workers were killed and 20 injured. He said eight insurgents died in the attack, which ended about midnight when the fighters retreated after taking some trucks.

"It is a very remote area, and there is no police presence there and we are investigating," said the provincial police chief, Gen. Abdul Ghafar Safi.

Galaxy Sky had a contract to build an 18-mile stretch of road through the mountainous area that was being funded by a NATO provincial reconstruction team, said Abdullah Durani, head of the public-works department of Paktia province.

Insurgents declared the start of a spring offensive against NATO and the Afghan government last month. NATO has been expecting the Taliban to stage a series of spectacular and complex attacks, and the group has carried out several.

On Wednesday, a suicide bomber crashed a car into a police bus in eastern Afghanistan, killing 14 people and wounding 16, the Interior Ministry said. Most of the casualties were police officers.

In southern Kandahar city, a roadside bomb killed a child and wounded eight others, including several children, the governor's office said Thursday, adding that the target was unclear.