(Adds two hurt in attack on aid agency office) By Zeeshan Haider ISLAMABAD, Feb 7 (Reuters) - Pakistani investigators tried on Wednesday to establish the identity of a suspected Islamist militant killed in a blast at Islamabad airport and questioned a man believed to be an accomplice. The incident late on Tuesday followed a wave of attacks including a Jan. 26 suicide bombing at a top Islamabad hotel and raised fears that Pakistan's war against Islamist militants in remote mountains on the Afghan border has spread to the capital. "The attack appears to have links to Waziristan," said a top government security official who declined to be identified because of the sensitivity of the case. The Waziristan region on the Afghan border is a hotbed of Islamist militancy where many al Qaeda and Taliban members took refuge after U.S.-led forces drove the Taliban from power in Afghanistan in 2001. Police were also questioning several people in connection with a separate grenade attack on a U.S. aid group in the northwest region on Monday in which two local employees were wounded, officials said. Pakistan, an important U.S. ally in the war on terrorism, has been trying to clear foreign militants out of North and South Waziristan and pacify their Pakistani allies. Hundreds of members of the security forces and militants have been killed in clashes but Islamabad -- a small, leafy capital nestled against the foothills of the Himalayan mountains -- has been largely free of militant violence in recent years. The man killed on Tuesday, who was bearded and appeared to be in his twenties, opened fire at security staff after they stopped a car he was in and tried to search him as he was attempting to get into the airport. The man, armed with two pistols, was killed when one of three grenades he was carrying went off in the airport car park. Interior Minister Aftab Ahmed Khan Sherpao initially said it was a suicide attack but security officials later said the man might have been killed when he accidentally dropped a grenade. Three security men were wounded. Two men in the car the attacker was travelling in, including the driver, were arrested. "We are interrogating the suspect," the security official said, referring to the passenger in the car. "We have gleaned some information but it is too early to divulge it." REVENGE ATTACKS? Pakistan has seen a spate of attacks, including several suicide bombings, in recent days that have killed nearly 30 people. The attacks followed a Pakistani air strike on an Islamist militant camp in South Waziristan on Jan. 16 that killed up to 20 people, raising widespread speculation among security analysts the blasts were in revenge for the strike. Intelligence officials have linked at least some of the latest attacks to pro-Taliban militants in Waziristan led by Baitullah Mehsud. President Pervez Musharraf last week described Mehsud as the only Taliban leader of importance based in Pakistan. Security in Islamabad has been much tightened in recent days with police stepping up patrols and checks on roads and at entrances to sensitive areas such as the diplomatic quarter. In a separate incident, at least one attacker fired shots and threw a grenade at a compound of the U.S. Save the Children aid group in Northwest Frontier Province, wounding two Pakistani employees, police and the group said. Police said they had questioned several people in connection with the Monday night attack but made no arrests. Some aid groups in the area, helping survivors of a devastating 2005 earthquake, have reported threats from Islamist militants opposed to aid groups helping women. (Additional reporting by Augustine Anthony)
