Anjem Choudary, head of the British branch of al-Muhajiroun (the immigrants), said Muslims living in Islamic states like Afghanistan and Pakistan had the right to "defend themselves against the aggressors."
Asked if he was encouraging Muslims in those countries to kill Blair, Choudary said: "Everything is possible in war, you do not make love, you make war."
The Muhajiroun's Pakistani-based spokesman, Abdel-Rahman Saleem, was quoted on Wednesday as saying: "Now, and after the British and American allies and probably the French have embarked on bombarding in Afghanistan, military installations and 10 Downing Street have become legitimate targets.
"He (Blair) has also become a legitimate target ... This means that if any Muslim wanted to kill him or to get rid of him, I would not shed any tears," Saleem told the London-based Asharq al-Awsat newspaper.
Choudary endorsed Saleem's statement, saying: "That is true about our members living in Afghanistan and Pakistan."
But Choudary said the group's 7,000 followers in Britain would not try to take the law into their own hands and would take no violent action in the country.
"Those of us living in non-Muslim countries are here as guests so we must support our brothers physically, verbally and financially by non-violent means. Anyway we are not armed."
Scotland Yard, which has been investigating the activities of al-Muhajiroun and its London-based founder Sheikh Omar Bakri Mohammed, said it was looking into Saleem's alleged comments.
"We continue to monitor comments made by the individuals and are in close consultation with the Crown Prosecution Service," it said.
Blair was in the Arabian Peninsula country of Oman on Wednesday to meet British troops on exercises in the desert and shore up support for the U.S-led "war on terrorism," launched over the September 11 suicide attacks on the United States.
U.S. and British forces have been pounding targets in Afghanistan, where the prime suspect in the attacks, Saudi-born dissident Osama bin Laden, is hiding.
The U.S.-led strikes have sparked protests in some Muslim countries, where the action is seen as a war against Islam.
Syrian exile Bakri, who founded al-Muhajiroun in 1983 when he was living in Saudi Arabia, told Reuters on Tuesday he was inspired by bin Laden though he had never met him.
"Bin Laden is right - this is a war against Muslims everywhere and the Islamic giant will rise again. We must rise and remove all the (Arab) dictators," he said.
Bakri has been in Britain since 1986 when he was expelled from Saudi Arabia for calling for the overthrow of the Saudi monarchy.
He claims to have followers in 15 countries, including Saudi Arabia, Kuwait, the United States, Pakistan and India. The Muhajiroun has branches in 25-30 British cities, hsays.
Britain's Crown Prosecution Service has been looking into Bakri's activities after he issued a fatwa, or religious edict, calling for the death of Pakistani President Pervez Musharraf for backing Washington.
The organization's leader said the remarks had been misinterpreted. Mohammed said he had spoken Wednesday to Saleem, "and he made it clear to me that he did not say Blair should be attacked.
"What he did was give the Pakistani perspective on Blair's visit to Pakistan" last week, Mohammed said. "And they see him as a leader who is sending armed forces to bomb and kill innocent civilians in Afghanistan.
"Here in the West, we live peacefully. It is against he law to make death threats."
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