NAIROBI, Kenya (CNN) -- A gray mist covered Nairobi like a shroud on Sunday and church bells pealed across the country in tribute to the dead as rescuers continued to comb through the rubble for survivors of Friday's devastating bomb blast outside the U.S. Embassy in Kenya's capital.

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Churches held special services and congregations prayed for nearly two dozen people still in critical condition in Nairobi's hospitals, and the Kenyan government made an international appeal for specialized medical help and supplies to treat the thousands of people injured in the explosion.

Reuters is reporting that the head of an Israeli rescue team on Sunday said his workers were trying to pull out a woman who appeared to be alive 48 hours after the blast.

"We have at this moment a woman trapped. We sent dogs to check 15 minutes ago if she's alive and according to our check she's still alive," Brigadier General Ilan Hariri told Israel Radio by phone from Nairobi.

"All our efforts, all our soldiers at this moment are working on rescuing her," Hariri said, adding his team had yet to detect other survivors.

An army radio reporter said from the rescue scene that workers had spoken to the woman several hours earlier but could no longer make contact with her. Another rescue worker said they needed a crane to reach the woman.

"We're trying to reach the location from the top. We're missing a big crane and that's delaying our access to her," Lt. Col. Nahum Frankel told army radio. Israel sent 160 rescue workers to Nairobi a day after the blast near the U.S. Embassy tore through the heart of the city on Friday.

Search dogs brought to the blast site Saturday by Israeli rescuers had indicated that there could be other survivors in the wreckage of Ufundi House, which was felled by the blast that heavily damaged the embassy.

The Israeli experts plucked a survivor out late on Saturday, nearly 36 hours after the bomb brought the building crashing down around him. The man had been in contact with the missing woman in the rubble, Israeli army radio said.

Meanwhile in neighboring Tanzania, where the U.S. Embassy also was rocked by an explosion Friday, employees returned to the damaged compound Saturday to salvage equipment and documents. Prime Minister Frederick Sumaye, who surveyed the scene, vowed that the bombers "will be caught ... and severely punished."

U.S. Marines threw a cordon around the bombed American embassy in Dar es Salaam on Sunday as teams of U.S. personnel began arriving in Tanzania.

After encircling the embassy with barbed wire, the Marines climbed inside the building and began removing documents, witnesses said.

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U.S. officials said investigators had been originally scheduled to arrive in Dar es Salaam on Saturday, but their flight was put back by one day. Another team is due in the city on Monday.

Embassy staff and Tanzanian police sealed off the Dar es Salaam embassy compound on Saturday and cordoned off nearby streets with yellow tape.

A strip of green tarpaulin was placed over the area where the bomb exploded in an apparent attempt to preserve evidence for future examination.

On Laibon Road outside the embassy a string of diplomatic cars were burned out, the embassy's visa section stood partially destroyed, while one side of the square, white, main building itself was scorched and damaged by the blast.

Tanzania's Vice-President Omar Ali Juma visited casualties at the capital's main hospital, Muhumbili Medical Center, on Saturday, according to witnesses.

Most of American dead identified

The death toll in Nairobi stands at 139, including 11 Americans. Nearly 4,300 people were hospitalized with injuries. In the Tanzanian capital of Dar es Salaam, 10 people died, none of them Americans. About 70 others were injured.

The State Department Saturday identified 10 of the 11 American victims. They include six members of the U.S. diplomatic corps: Jean Dalizu, Molly Hardy, Parbhi Kavaler, Arlene Kirk, Michelle O'Connor and Tom Shah; three members of the U.S. military: Marine Sgt. Jesse Aliganga, Army Sgt. Kenneth Hobson II and Air Force Senior Master Sgt. Sherry Lynn Olds; and Jay Bartley, the son of the embassy's consul general, Julian Bartley.

U.S. Ambassador Prudence Bushnell said five Americans are still missing, as are 109 Kenyans who worked at the embassy.

Kenyan President Daniel arap Moi said on Sunday that investigators were pursing several leads into the Nairobi bombing.

Asked during a tour of the site whether police had any leads, Moi said: "Yes, we are pursuing several clues."

On Saturday, U.S. officials downplayed a claim of responsibility for the bombings received by a London-based Arabic language newspaper, Al-Hayat.

An unidentified caller claiming to be with a group called "The Islamic Army for the Liberation of Holy Places" called the newspaper's Cairo office Friday, claiming responsibility for the blasts. The group was previously unknown.

Similar statements were sent to Qatar's al-Jazirah Satellite Channel and Radio France International. But the State Department says it does not consider the claims to be credible.

Kenya asks for pathologists, plastic surgeons

In the face of the carnage in Nairobi, the Kenyan government made an appeal Saturday for specialized medical help. Its charge d'affaires in Washington, Felistas Khayumbi, said pathologists and plastic surgeons are needed, as well as drugs, blankets, sheets and mattresses.

She said Kenya had already received many offers of assistance.

"Almost everybody has come in to help us. Red Cross is there, many other international communities," she said. "Other countries are all coming in with their support."

Seven U.S. support flights, bearing medical and security personnel and investigators, are scheduled to make the journey to East Africa.

About 60 U.S. investigators were being dispatched to Kenya and Tanzania to try to find out who is responsible for what U.S. officials believe were coordinated terrorist attacks.

The two bombs went off within minutes of each other. Nairobi and Dar es Salaam are about 450 miles (720 km) apart.

Bushnell said the United States as of yet has no idea who might be responsible. But in a radio address Saturday, U.S. President Bill Clinton vowed that "no matter how long it takes or where it takes us, we will pursue terrorists until the cases are solved and justice is done."

CNN Correspondents Jerrold Kessel, Catherine Bond, Ben Wedeman and Louise Schiavone and Reuters contributed to this report.