ISLAMABAD — The death toll from a massive earthquake that struck southwestern Pakistan this week rose to 357 Thursday, as security concerns in Baluchistan province impaired efforts by search crews to reach tens of thousands of stranded citizens.

Members of the paramilitary Frontier Constabulary force were busy on rescue operations in Awaran, the worst-hit district, Thursday afternoon when they came under attack by militants, military officials said. The attackers were repelled with no loss of life, they said, without providing more details.

Rebels also fired two rockets at a relief helicopter carrying a military commander and a disaster relief official, officials said, although no one was hurt.

In response, rescue teams including more than 1,200 military and paramilitary troops have restricted their movements, local media reported. Abdul Malik Baloch, the chief minister of Baluchistan province, appealed to the rebels to stop attacking relief convoys.

Relief agencies said Thursday that 620 people were injured in addition to the 357 dead, according to their latest tally.

An insurgency has operated for a decade in Baluchistan, Pakistan's largest but least populated province, hoping to create a separate Baluch-speaking state. In recent years, groups such as the Baluch Liberation Army and Baluch Liberation Front have targeted army facilities and pro-government politicians. The province is one of the poorest in Pakistan.

Gohram Baloch, a spokesman for Baluchistan Liberation Front, said this week that his group would attack officials of the government agencies in order to spread panic.

Rescue teams are yet to reach some isolated parts of Baluchistan, which was hit by the 7.7-magnitude temblor Tuesday, given the hostile terrain, security concerns and poor or nonexistent roads. More than 100,000 people left homeless by the widespread destruction of mud and brick homes spent a second night in the open as emergency crews scrambled to transport food, water and medical supplies to the worst-hit areas.

Concerned with the delay in relief operations, Prime Minister Nawaz Sharif ordered authorities to deploy more helicopters and C-130 transport aircraft, according to state-run Radio Pakistan. The earthquake destroyed or damaged more than 20,000 houses, a disaster management agency said, amid reports that entire villages were brought down.

The quake is reportedly Pakistan's deadliest since a devastating temblor in Kashmir in 2005 that killed more than 74,000 people.

Frustration has mounted in communities where relief has been slow or hasn't arrived at all. About 100 angry survivors protested outside government offices in the town of Arawan on Thursday, complaining that they had not received food or shelter.

Temperatures in the area reached 108 degrees as survivors struggled without tents, food or water.