He said they "stood for everything that is right about our country and the world - Americans and Africans, working together for peace and progress and a better future".

More than 200 people were killed in the attacks, including 44 Kenyans and Tanzanians working in the buildings, and 12 Americans.

The US president pledged to prevail against those behind the bombings, which Washington blamed on a terrorist cell linked to Saudi dissident Osama bin Laden.

"In the end, we will prevail against terrorism because the spirited dedication of men and women like those who perished last 7 August lives on.

"No bullet or bomb can ever destroy it."

Ceremonies

Kenyans and Tanzanians are themselves preparing for a national day of mourning to mark the first anniversary of the bomb attacks.

The Nairobi bomb demolished nearby buildings

A wreath-laying ceremony in memory of the victims will be held on Saturday at the site of the Nairobi attack, in the heart of the capital's business district.

A minute of silence will be observed at 1040 local time, the time of the blast.

The US embassy says it will be holding a private ceremony for the families of Kenyan and American victims. Some relatives of US victims have returned to Kenya to mark the day.

A US official said it was appropriate to keep the commemoration as a low-key, extended-family event both for security reasons and out of respect for Kenyans who died in the attack.

Memorial plaque

In the Tanzanian capital Dar es Salaam - scene of an almost simultaneous attack - a ceremony was held on Friday to dedicate a plaque carrying the names of all those killed in both bombings.

The plaque was unveiled in the presence of US Ambassador Charles Stith by the children of three people killed.

Ambassador Stith announced that the plaque would be housed at a new embassy to be built as soon as possible in the Tanzanian capital.

Other ceremonies were expected to take place in the city over the weekend.

'Callous act'

In Nairobi on Friday, the Supreme Council of Kenyan Muslims said special prayers were being held in mosques throughout the country.

The chairman of the council, Abdulghafur El-Busaidy, condemned what he called "a most callous act by people who had turned from the righteous path".

A memorial service will take place at the site of the bombing

Prayer services will be held across the city and later in the weekend an open-air concert will be staged with performances from Kenyan, European and US musicians.

However local organisers of an interfaith memorial service say an American-based evangelist is threatening to overshadow Kenya's national remembrance of the event with a global peace rally.

They say the rally organised by Kilari Anan Paul threatens to shift attention away from the Kenyan victims of the bombing.

However Mr Paul, who says he has been "in constant touch" with Kenyan President Daniel arap Moi, has insisted the Kenyan victims will remain the focus of the occasion.

Correspondents say Mr Moi's decision to allow a foreigner to manage the main memorial ceremony for what many Kenyans consider a national tragedy has raised a few eyebrows.