Police were searching for the culprits and it was unclear if any of the Islamist protesters were involved, said Basharat Mahmood, police chief in the eastern city of Gujarat where the attack occurred.
“It is surely a terrorist attack,” said Mahmood. “The attackers could have taken cover. They could have hid themselves among the protesters.”
The camp on the outskirts of Gujarat was attacked at around 5:20 a.m., a little less than an hour after the leaders of the Difah-e-Pakistan, or Defense of Pakistan, protest movement finished delivering speeches inside the city, said the police.
The group, which includes hardline Islamist politicians and religious leaders, left the city of Lahore on Sunday along with 8,000 supporters in 200 vehicles to make the 300-kilometer (185-mile) journey to Islamabad. They traveled about halfway, spent the night in Gujarat and plan to hold a protest in front of parliament in the capital on Monday.
The roughly half dozen gunmen who attacked the camp were riding in a car and on motorcycles. They killed seven soldiers at the camp and a policeman who tried to intercept them as they were escaping, said Mahmood, the police chief. Four policemen and at least three soldiers were wounded, he said.
The camp that was attacked was set up to look for the body of an army major who was flying a helicopter when it crashed into a river in the area, said the police.
The leaders of Difah-e-Pakistan include people with known militant links, including Hafiz Saeed, the founder of the banned Lashkar-e-Taiba militant group, and Maulana Samiul Haq, known as the father of the Taliban.
But they are not known to be supporters of the Pakistani Taliban, who have waged a bloody insurgency against the state over the past few years and killed thousands of soldiers and police.
Many of the Difah-e-Pakistan leaders have strong historical links with Pakistani intelligence, and the group is widely believed to have been supported by the army to put pressure on the U.S. while the government negotiated over the NATO supply line.
Pakistan closed the route in November in retaliation for American air-strikes that killed 24 Pakistani soldiers. The government finally agreed to reopen the supply line last week after the U.S. apologized for the deaths.
One of the reasons Pakistan waited so long to allow NATO troop supplies to resume was that it was worried about domestic backlash in a country where anti-American sentiment is rampant.
Difah-e-Pakistan leaders said Sunday that they were holding their so-called “long march” to Islamabad to prevent Pakistan from becoming a slave to the U.S. and to show that many citizens are unhappy with the decision to reopen the route.
But the number of protesters has been relatively small so far given Pakistan's population of 190 million, and the demonstration is unlikely to have any effect on the government's decision.