PESHAWAR, Pakistan, (Reuters) – Authorities have arrested one man over a suicide attack at a mosque in northwest Pakistan that killed 48 people, and said they suspect Islamic militants in an Afghan border region were involved.

Police picked up the suspect in Charsadda, security officials said, the same district where a suicide bomber detonated 8-10 kg (18 to 22 lbs) of explosives on Friday in the midst of a packed 1,000-strong congregation celebrating the festival of Eid. “We’re looking for another man who could be a second accomplice,” a security official, who asked not to be named, told Reuters.

Local residents and television said four people, including three Afghan nationals, were arrested late Friday in a town four km (2.5 miles) from the site of the attack near Peshawar, capital of North West Frontier Province. It was unclear if the detentions were related to the blast.

Former interior minister, Aftab Ahmed Khan Sherpao, who is a leading supporter of President Pervez Musharraf, was offering Eid prayers at the mosque at the time of the blast. He survived unhurt but at least 80 people were wounded.

Police believe Sherpao, who survived another suicide attack in April, was the likely target.

Provincial police chief Sharif Virk and intelligence officials told Reuters the attack could be linked to militant groups in the adjacent Mohmand tribal region, a lawless area that straddles the border with Afghanistan.

Many al Qaeda and Taliban members took refuge in remote regions on the Pakistani side of the Afghan border after U.S. and Afghan opposition forces toppled the Taliban government in Afghanistan after the Sept. 11 attacks on the United States. “We suspect that it could be orchestrated in Mohmand tribal agency, from where we suspect the previous attack on Sherpao was planned,” the security official said.

U.S. Defense Secretary Robert Gates said on Friday that al Qaeda has regrouped in Pakistan’s remote Afghan border area and begun to focus attacks on the Pakistani government and military. Virk said that so far forensic evidence at the site of the blast was insufficient to give up any strong leads. “No head has been found from the scene,” he said, referring to the fact that the heads of suicide bombers are often blown off by the force of the explosions and later found intact. “We have found four legs which we have sent for DNA test, but it could be little help unless we know the family.” There has been a rash of suicide attacks blamed on Islamist militants since a military assault on the Red Mosque, a militant stronghold in Islamabad, in July.

More than 800 people have been killed in the ensuing violence across the country, about half of them in suicide attacks.

Musharraf, an important ally in the U.S.-led war on terrorism, cited growing militancy as a main reason behind his imposition of emergency rule on Nov. 3.

Hours after lifting emergency rule last weekend, Musharraf said his government had “broken the back” of the militancy.