CBS News Radio Correspondent Steve Holt reports over 700 officers took part in the raids in London and its nearby suburbs. Peter Clarke, the head of Scotland Yard's anti-terrorism branch, says they found a thousand pounds of ammonium nitrate in a west London storage facility.
Clarke says all the suspects are British and were arrested as part of an operation targeting alleged international terrorist activity.
Clarke also says the operation does not appear to be connected to either the Madrid train bombs earlier this month or terrorism by the Irish Republican Army.
Ammonium nitrate is a common fertilizer, but it can be mixed with fuel oil to make a powerful explosive. It was used in the Oct. 12, 2002 blast in Bali that killed 192 people, mostly Western tourists.
Clarke says early morning raids targeted residences and business properties. The ammonium nitrate was recovered from a self-storage facility in west London.
Authorities say the suspects - men aged 17 to 32 - were arrested on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism.
Two suspects were arrested in Uxbridge, also in west London, and three in Crawley, south of the capital. One was detained in Ilford, east London, another in Slough, west of London, and another in Horley, south of the capital.
Officers conducted a total 24 searches that also targeted addresses in Reading, Luton and north London.
Clarke gave no details of the religious affiliation of the suspects, but he told reporters: "As we have said on many occasions in the past, we in the police service know that the overwhelming majority of the Muslim community are law abiding and completely reject all forms of violence. We have a responsibility to all communities to investigate suspected terrorist activity."
Ammonium nitrate was used to make a bomb in a van that was parked near the U.S. Consulate in Karachi, Pakistan, on March 15. It did not explode.
The substance was also used in a suicide bomb attack in which an explosives-laden truck was detonated outside a British bank in Istanbul, Turkey in November.
In years past, the Irish Republican Army used ammonium nitrate in attacks in London and in Northern Ireland.