NAIROBI, Kenya (AP) _ Powerful bombs exploded outside the U.S. embassies in Kenya and Tanzania today, toppling a four-story building and killing more than 50 people. More than 1,000 were injured, officials said.

The American ambassador to Kenya was slightly injured.

``It was definitely a bomb,'' said a U.S. Embassy official in Nairobi, who refused to give his name. ``You can see a huge crater behind the building, and a bomb went off at the embassy in Tanzania at the same time.''

The blast in Nairobi at 10:35 a.m. (3:35 a.m. EDT) toppled the four-story Ufundi Cooperative building toward the embassy, which was badly damaged. Cooperative Bank House, with government and private offices, also was damaged.

Rescuers clamored atop a tangle of concrete and metal bars, clawing through wreckage to try to reach dozens of trapped people.

More than 40 were killed and more than 1,000 wounded in Nairobi alone, the Red Cross said.

``Once the rubble is cleared further we expect to find more,'' said Red Cross worker Nina Galbe. Added another Red Cross worker who refused to give his name: ``There are too many dead to count.''