The bodies of 11 U.S. citizens killed in the Kenya blast arrive in Germany
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(CNN) -- As the grim work of rescue efforts continued into the night in Kenya and Tanzania, U.S. investigators on Monday pursued leads in their investigation of two deadly U.S. embassy bombings.

The bodies of 11 Americans killed in the Kenya bombing also began the long trip home Monday, and the United States offered a $2 million reward for information leading to the conviction of the bombers.

In the Nairobi bombing, sources told CNN that authorities now believe a truck -- possibly a Mitsubishi -- pulled up to the U.S. embassy's front entrance but guards told the driver that it could not enter there.

The truck then reportedly drove to the embassy's rear entrance where the driver again met resistance. There are reports that shots were fired and someone in the truck allegedly threw a grenade.

"Someone either waved or threw hand grenades at (a guard). He refused to open the gate. When the hand grenades came, of course, he ran away to save himself. The blast went off, knocked him down, and he survived," said Thomas Pickering, U.S. Undersecretary of State for Political Affairs.

The Kenyan guards "did a heroic job in preventing the truck that approached the rear gate of the embassy in gaining access to the embassy," Assistant Secretary of State Susan Rice for African Affairs said.

"Clearly, according to our reports, (they) had every intention of getting inside the compound, and had they gotten inside, particularly underneath the garage, the damage to our facility and to our people would have been even greater," Rice said.

Foreign Service officers undaunted by bombings Mideast, African embassies tighten security after bombings Protecting embassies difficult ... and probably impossible U.S. victims in Friday's bombing in Nairobi, Kenya Chronology of attacks on U.S. targets Image gallery Message board: Africa explosions

The Tanzanian government said Monday it has detained "three groups" of suspects in the nearly simultaneous bombing of the embassy there. A U.S. official who asked not to be identified said the suspects were mostly Iraqi and Sudanese nationalities.

"We hope this is a break in this case," said Rice in an interview with CNN in Washington. But she also said that people should not attach too much importance to the detainees.

Police believe that the bomb in Tanzania was planted in a blue tanker truck that regularly delivered water to the embassy. It was about to enter the compound when it exploded.

A U.S. diplomat who declined to be identified said a surveillance camera at the embassy was operating at the time of the explosion. But he would not say whether the camera was taping or was simply being monitored in real time by embassy security.

The bodies of 11 Americans killed in the blast arrived Monday at Ramstein Air Base in Germany. The 12th American victim, Jean Dalizu, was married to a Kenyan and will be buried in her adopted homeland.

From Ramstein, the bodies will be flown to Andrews Air Force Base in Maryland.

As each of the flag-draped aluminum coffins was lifted into the U.S. Air Force C-141 aircraft in Nairobi, U.S. Ambassador Prudence Bushnell raised her right hand -- still bandaged from the injuries she suffered in the Friday blast -- to her heart.

Kenyan Foreign Minister Bonaya Godana stood at attention nearby.

U.S. Marine and Navy honor guards carried 10 of the coffins, and a special Marine unit in camouflage uniforms carried the coffin of fallen comrade Sgt. Jesse N. Aliganga of Tallahassee, Florida.

Rescuers on Monday continued their grim search for possible survivors in Nairobi. In the Kenyan bombing, 192 people were killed, including the 12 Americans, and nearly 5,000 were injured.

Rescue personnel in Nairobi try to make contact with Rose, a woman trapped in the rubble for three days

However, the death toll is expected to rise in Kenya, according to International Red Cross officials. They believe more bodies lie beneath the destroyed embassy.

At least 10 died in Dar es Salaam, and 74 others were injured there.

In Nairobi, search and rescue workers on Monday briefly halted their operation because of fears that a 22-story building damaged in the blast might collapse. But after about 45 minutes, they were back at work.

Kenyan Red Cross workers say they believe that a woman named Rose and possibly another named Jane might still be alive in the ruins of the collapsed Ufundi Cooperative House, adjacent to the U.S. Embassy in Nairobi.

"I am full of hope she is alive and is hanging in there," said Meital Hallawi, an officer in the Israeli army rescue unit.

Israeli rescuers, who were using a 150-ton crane, drills and blowtorches, said they heard tapping inside the Ufundi building Monday morning, spurring them on in their search for Rose. A sophisticated listening device was lowered into the wreckage to see if she was still breathing.

"As long as there is the slightest chance of any person being found alive, every moment up there is precious," said Nina Galbe, a spokeswoman for the International Committee of the Red Cross.

Gerard Bradford, head of a disaster response team from the United States, said his team was searching for nine missing Kenyan employees.

"There is hip-deep debris in a lot of those rooms," he said.

FBI crews investigate the wreckage of several vehicles destroyed in the Kenyan blast

Pickering said that 150 FBI agents were now at work in Nairobi and Dar es Salaam as part of investigation efforts to find out who was behind the attacks and how they were carried out.

As part of the investigative efforts, U.S. pathologists on Monday carried out autopsies on the corpses of those killed in the Tanzania blast. Later in the day, they began releasing the 10 bodies to their families.

The United States also announced Monday that it is offering a $2 million reward for anyone who provides information leading to the arrest and conviction of those responsible for the bombings.

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