Police seized various items in the raids last Thursday

The suspects - arrested in Bursa - were members of the radical Islamic group Ansar al-Islam, believed to have links to al-Qaeda, police said.

Guns, explosives, bomb-making booklets and 4,000 CDs with training advice from Osama Bin Laden were also seized.

US President George W Bush and other world leaders are due at the summit which will be held on 27 and 28 June.

Summit worries

The Turkish state security court charged the nine with "membership in an illegal organization" - a charge carrying a sentence of up to 10 years in prison.

Seven of the 16 suspects arrested in Bursa, a city about 250km (160 miles) south of Istanbul, were released earlier. Nine held in Istanbul had already been freed.

"The organisation has been neutralised in a successful operation while in the stage of planning attacks," Bursa governor Oguz Kagan Koksal was quoted as saying by Turkey's Anatolia news agency.

With up to 50 world leaders scheduled to attend, Turkey is under pressure to ensure security is water-tight for the Nato summit.

Fears of attacks have been heightened since the four suicide bombings in Istanbul last November.

Sixty-two people were killed and hundreds injured when two synagogues, the British consulate and HSBC bank were targeted in Turkey's largest city.

But Istanbul's Governor, Muammer Guler, insisted the city was safe.

"There is no question of a situation that will affect the meeting," Mr Guler said.