London ? Prime Minister Tony Blair appealed to Muslim leaders on Tuesday to combat the “twisted logic” of terrorism and offered to help them counter extremism with reason. In a show of vigilance, police deployed dogs for the first time to sniff out explosives on London’s Underground.

The developments in London came as police in Pakistan detained as many as 50 men Tuesday in a fourth day of searches and raids, many of them as part of the bombing investigation. And in Cairo, the Egyptian government said a detained chemist wanted for questioning by Britain had no links to the attacks or to al-Qaida.

British officials were also examining whether bomber Jermaine Lindsay, a Jamaican-born Briton, used perfume bottles to make his bomb deadlier. The explosions on three subways and a double-decker bus in London killed at least 56 people.

Asked about the inquiry into the July 7 attacks by Lindsay and three other bombers, Ian Blair, chief of the Metropolitan police, said key questions remain, including: “Who is the chemist? Who are the people who trained them? Who facilitated their trip to Pakistan?”

“Whoever is doing that is still out there,” the police chief told a meeting of Christians, Muslims and Jews that was attended by The Associated Press.

Fearful of another attack since accomplices of the bombers or a mastermind may be at large, British Transport Police dispatched dogs Tuesday to search for explosives on the London Underground.

Dogs have been used before on the train that connects Heathrow airport to the capital, but police said this was the first time they were being sent into the subway system.

Tony Blair met with two dozen representatives of the Muslim community to discuss anti-terror legislation the government plans to introduce by year’s end. The leaders fear the laws target their community.

“It’s fair the government should ask itself whether policies such as those involving the Iraq war have contributed to this,” said Dr. Zaki Badawi, head of the Muslim College. “We need a partnership between government and Muslims to show people they are not being ignored and that their concerns will be heard.”

The prime minister denied any link between the Iraq war, which was opposed by many Britons, and the attacks in London. He insisted terrorists would always find an excuse to kill – and promised action to uproot their “perverted ideology.”

“Of course these terrorists will use Iraq as an excuse. They will use Afghanistan,” Blair said at a news conference after meeting with Afghan President Hamid Karzai.

“Sept. 11, of course, happened before both of these things, and then the excuse was American policy, or Israel. They will always have their reasons for acting,” Blair said. “But we have got to be really careful of almost giving in to the sort of perverted and twisted logic with which they argue.”

Karzai agreed. “There is no link,” he said. “They are simply merchants of death.”