The head of the UN atomic watchdog Mohamed ElBaradei has voiced concern over the possibility that Pakistan's nuclear arsenal could fall into extremist hands, in statements published on Tuesday.

"I fear that chaos... or an extremist regime could take root in that country which has 30 to 40 warheads," ElBaradei told the pan-Arab daily Al-Hayat in an interview.

He stressed that he was "worried that nuclear weapons could fall into the hands of an extremist group in Pakistan or in Afghanistan."

There has been worldwide concern over the security of Pakistan's estimated 50 nuclear warheads since Pakistan President Pervez Musharraf imposed a state of emergency in the troubled country in November.

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Musharraf said in December that Pakistan's nuclear weapons were under control.

Tensions have been running high in the Islamic country since the December 27 assassination of opposition leader Benazir Bhutto after an election rally.

"I fear that a war in the Middle East or in the Muslim world could have grave repercussions in Pakistan, more than in Iran," ElBaradei said.

The UN nuclear chief, who is due to visit Tehran at the end of this week for talks on Iran's disputed nuclear programme, reiterated warnings against any attempts to solve the problem by force.

"Any attack on Iranian nuclear facilities will only complicate the problem," he said.

The United States wants the UN Security Council to impose a fresh package of sanctions against Tehran, although a recent US intelligence report said Iran halted a nuclear weapons programme in 2003.

The US intelligence "provides an opportunity for a peaceful dialogue to solve the problem through negotiation," ElBaradei said.

US President George W. Bush, on a visit this week to the region, is due to urge Arab states to put pressure on Iran over its nuclear programme, which Tehran says is entirely peaceful.

ElBaradei also told Al-Hayat the Syrian authorities did not authorise international inspectors to visit a site bombed by Israel last September.

Speculation ran high in the US and British media after the September 6 attack that the site may have been used to store nuclear materials from North Korea. Syria denied the allegations.