Some security officials and relief groups are coming under attack as they struggle to reach victims in earthquake-ravaged southwestern Pakistan, demonstrating the volatile conditions in areas hardest hit by Tuesday’s 7.7-magnitude temblor.

As rescue efforts continued for a third day, officials reported at least 355 fatalities and more than 600 injuries in the country’s restive Baluchistan province. But many areas remained inaccessible Thursday, raising fears that the death toll could be far higher.

The quake was centered near an impoverished area where many homes are built of mud and stone. The area is also home to several insurgent and militant groups, some of which have been fighting Pakistan’s army for years.

“Roads are nonexistent in some areas, so aid is airlifted to such places, and helicopters and C-130 planes are being used for that,” Pakistani Interior Minister Chaudhry Nisar Ali Khan said in a speech to the National Assembly on Thursday. “We fear the death toll could rise, as we still have to reach out to some far-flung areas.”

But rescue efforts slowed Thursday when an army helicopter carrying two high-ranking generals came under rocket fire near the province’s Awaran district, where an estimated 20,000 homes have collapsed.

Maj. Gen. Muhammed Saeed Aleem, chief of Pakistan’s National Disaster Management Authority, and Maj. Samraiz Salik, who heads the army’s relief operations, escaped injury.

“Two rockets were fired from the ground, but fortunately didn’t hit the helicopter,” said a Pakistani official, who spoke on the condition of anonymity because he was not authorized to talk to the media.

There have also been reports of gunfire aimed at army and relief officials on the ground, raising concerns about whether the area is safe enough for international relief organizations.

“These are troubled regions . . . and we have heard about security concerns among the [nongovernmental relief groups] operating there,” Bijar Khan Marri, a spokesman for the Pakistan Red Crescent Society, said in an interview. “However, as an independent relief organization, we are just hoping we will not face any trouble out there. I believe the people know we are there for relief.”

Despite the attacks, Pakistani army commanders say they will continue to provide assistance. Earlier Thursday, additional troops arrived in the region from Karachi. By nightfall, army officials said about 500 injured people had been evacuated from the area.

But Essa Noori, a member of the national assembly from Baluchistan, said he fears that Pakistan’s military response will not be enough to prevent further loss of life. Noori said international help is needed, adding that concerns about security are overblown. “Yes, there are some scattered incidents, but the security issue is not and should not be a hurdle in the way of relief and rescue operations,” Noori said. “The international humanitarian organizations should come and help the earthquake-affected people.”

Baluchistan is Pakistan’s largest but least populated province and has been isolated for years because of an ongoing conflict. Separatist groups, including the Baluch Liberation Army and Baluch Liberation Front, have been fighting Pakistani security forces since at least 2004. The groups hope to create a separate state for Baluch-speaking residents. In recent years, the separatists have targeted Pakistani army installations and pro-government politicians.

The province also is home to a dominant Pashtun population, and Islamist militant groups such as the Taliban and Lashkar-e-Jhangvi, an affiliate of al-Qaeda, have found havens in its Pashtun areas. These militants also attack security officials, as well as the Shiite Muslim minority and convoys supplying the NATO mission in neighboring Afghanistan.

Despite the dangers, U.S. officials say they are evaluating what kind of assistance they may be able to offer to the recovery effort.

Khan, the interior minister, said damage from Tuesday’s earthquake spans about 300 miles.

Mumtaz Baloch, a senior local official in the hard-hit Awaran district, said 12 trucks of relief supplies have reached the area. A 31-member team of doctors is also operating there. But Baloch said thousands of people still need food and medicine.

In addition to the 20,000 homes flattened in the Awaran district, at least 1,000 homes have collapsed in the province’s Kech district, officials said.

“The government is trying its best to provide relief,” Khan told the National Assembly.

United Nations Secretary General Ban Ki-moon said through a spokesman the U.N. “stands ready to lend assistance to respond to humanitarian needs resulting from the earthquake and to mobilize any international support needed.”

The World Health Organization has already provided Pakistani authorities with enough emergency kits to treat more than 100,000 people. The U.N. World Food Program has also arranged for “high-energy biscuits” to be delivered to the area to to stave off starvation, officials said.

Haq Nawaz Khan contributed to this report.