Bush: Terror threat growing

Bush warned of an "unprecedented threat"

US President George W Bush has issued another warning about the growing danger of terror groups gaining access to weapons of mass destruction.

He said terrorists could wield "catastrophic power" with the spread of nuclear and biological weapons technology.

Abdullah al-Muhajir was jailed in the 1990s

His remarks follow news on Monday that the US authorities had foiled an alleged plot by al-Qaeda to detonate a "dirty bomb" containing radioactive material in the US.

The authorities in Morocco were also reported to have uncovered an al-Qaeda plan to attack US and UK naval ships in the Straits of Gibraltar.

Officials there were quoted as saying that three Saudi men had been arrested in May in connection with the plot.

Al-Qaeda 'active'

US Attorney General John Ashcroft announced on Monday that a US citizen, Abdullah al-Muhajir, had been arrested on 8 May at Chicago airport after arriving from Pakistan.

The suspect is alleged to have been planning to build and explode the bomb, which can spread material highly toxic to humans.

Investigators are said to have known about Mr al-Muhajir for some time. Officials said he was stopped in the "initial planning stages" and no specific targets had been selected.

BBC world affairs correspondent Frank Gardner says the alleged plot shows al-Qaeda is "alive and active" and will be an enormous boost to the organisation's supporters in the Middle East because it shows they can still attempt to mount operations against the US.

Planning stage

Mr Ashcroft said that 31-year-old Mr al-Muhajir posed a serious and continuing threat and was in the custody of the US military after having been held by the Justice Department in New York for a month.

How does a dirty bomb work?

A conventional bomb is packed with radioactive isotopes

The force of the explosion spreads radioactive material over a wide area

Likely to cause radiation sickness in any exposed to the contaminated area

Massive disruption ensues

Read more about dirty bombs

His activities and association with al-Qaeda qualified him as an "enemy combatant", Mr Ashcroft said.

Mr al-Muhajir has been taken to a high security US Navy prison in Charleston, South Carolina, officials said.

Then known as Jose Padilla, Mr al-Muhajir was in prison in the US in the early 1990s, reportedly for his part in the activities of Chicago street gangs.

He was also put on a year's probation in Florida for aggravated assault and firing a weapon.

He is believed to have converted to Islam while in prison, and then left the country in 1998, visiting Afghanistan and Pakistan in 2001.

Zubaydah claim

It was there that he met al-Qaeda officials, Mr Ashcroft said, adding that he "trained with the enemy, including studying how to wire explosive devices".

Bin Laden: May be able to build dirty bombs

Al-Qaeda apparently believed that - as a US citizen - Mr al-Muhajir would be able to travel freely throughout the country.

In April, Abu Zubaydah, a senior aide to Osama Bin Laden captured by the US, reportedly told interrogators that al-Qaeda had the capability to build a dirty bomb and smuggle it into the US.

Radiological dispersion devices consist of conventional explosives wrapped with radioactive waste which can be found in hospitals and industrial plants.

BBC science correspondent Tom Heap says such materials are much more widely available than weapons-grade material, and are kept in conditions no more secure than the average high street bank.