NASA launched an investigation into the disaster and began searching for the astronauts' remains. It said that although there had been some data failures it was too early to nail down a precise cause.

The break-up, 16 minutes before the shuttle was due to land at Kennedy Space Center in Florida, spread possibly toxic debris over a wide swath of Texas and neighboring states.

With the United States jumpy about the countdown to possible war with Iraq and an Israeli astronaut included in the shuttle crew, officials discounted terrorism. "At this time we have no indication that the mishap was caused by anything or anyone on the ground," NASA administrator Sean O'Keefe said.

Dramatic television images of the shuttle's descent clearly showed several white trails streaking through blue skies after the shuttle suddenly fell apart.

It was almost 17 years to the day that the Challenger shuttle exploded on Jan. 28, 1986, killing all seven astronauts on board. In a poignant moment, astronauts on board Columbia had observed a minute's silence in their memory on Tuesday.

Take-off and re-entry into Earth's atmosphere are the most dangerous parts of a space mission. In 42 years of US' human space flight, there had never been an accident in the descent to Earth or landing. Challenger exploded just after take-off.

NASA officials at the Johnson Space Center in Houston said there had been a loss of key data transmissions from the left side of the orbiter just before the disaster.

Rescue teams scrambled to search for the remains of the crew, which included the first Israeli to fly on the shuttle, former combat pilot Col. Ilan Ramon. There were warnings that parts of a vast 120-mile-long corridor of debris could be toxic because of poisonous rocket propellant.

CNN said a family reported finding a leg in a field in Hemphill, Texas. Investigators later carried a black body bag from the area and placed it into the back of a hearse as they bowed their heads.

"We are not ready to confirm that we have found any human remains," Nacogdoches County Sheriff Thomas Kerrs said.

He added that among the roughly 1,000 calls reporting debris, some people said they found remains of crew members.

"The Columbia is lost. There are no survivors," said a grim-faced Bush in a message broadcast on television, which included condolences to the families of the dead astronauts. "Our entire nation grieves with you."

Israeli Astronaut, Huge Security

VIPs who were lined up to greet the returning astronauts at Kennedy Space Center in Florida were led away from a grandstand near the shuttle's landing strip by NASA officials after reports of the break-up.

Israelis and Americans watched their televisions in shock as details of the space craft's fate unfolded.

A huge security operation had been mounted to protect the take-off of Columbia on Jan. 16 because of terrorism fears and the presence of the Israeli astronaut.

Bush telephoned Israeli Prime Minister Ariel Sharon to lament a "tragic day for the astronauts' families and a tragic day for science."

Administration officials said at such a height the shuttle was out of surface-to-air missile range, and no threat had been received targeting the spacecraft.

NASA, which was assembling debris from the shuttle for its inquiry, put future shuttle flights on hold until it had worked out the cause of the Columbia loss.

Bush, who ordered American flags to be flown at half-staff as a mark of respect for the crew, said the crew "did not return safely to Earth, yet we can pray that all are safely home," in remarks recalling religious imagery used by President Ronald Reagan about the Challenger.

At the Vatican, Pope John Paul prayed for the dead astronauts during a mass at St Peter's Basilica. Condolences poured in from the leaders of a raft of countries including Britain, France and Germany.

NASA lost contact with the shuttle, which was completing a 16-day mission, at around 9 a.m. EST while it was 207,000 feet above Earth.

"The first indications of a potential problem occurred minutes before 8 o'clock central standard time. The first indications were of the loss of sensors, temperature sensors in the hydraulic systems on the left," Ron Dittemore, shuttle program manager, said at Johnson Space Center.

"They were followed seconds and minutes later by several other problems, including loss of tire pressure indications on the left main gear," said Dittimore who summed up the mood at the center by saying: "We're devastated."

On Friday, NASA flight entry director, Leroy Cain, was asked about possible damage to the left wing of the orbiter which might have occurred on lift-off. He said analyzes by NASA engineers had shown any damage to be minor, adding: "We're not working any concerns on the orbiter."

There were many reports from local residents of the shuttle breaking apart and of a loud "boom."

Disaster Raises Questions About Space Travel

The accident is likely to raise questions over the longevity of the shuttle fleet as Columbia was NASA's oldest shuttle and first flew in 1981. It was 32 months after the Challenger disaster before NASA flew a space shuttle again.

It also raised questions about the resupply of the International Space Station. The shuttle is the main resupply vehicle for the outpost in space.

Bush was grieving for the astronauts but adamant. "The cause in which they died will continue," he said, adding: "Our journey into space will go on."

The rest of the Columbia crew were Americans -- Mission Commander Rick Husband, Pilot William McCool, Payload Commander Michael Anderson, Mission Specialist David Brown, Mission Specialists Laurel Clark and Indian-born Kalpana Chawla.

Ramon was listed as a payload specialist. Ramon's mother was a Holocaust survivor from the Auschwitz concentration camp. In memory of family members who did not survive the Nazi rule of World War II, Ramon took with him a pencil drawing by a Czech Jewish boy.

There was mounting concern about toxic chemicals from the debris. NASA mission control in Houston said, "Any debris that is located in the Dallas-Fort Worth vicinity should be avoided and may be hazardous."

Nacogdoches, Texas, received one report of the finding of what appeared to be a door from the orbiter.

"We do have a debris field. It is scattered all throughout Nacogdoches," said Victoria Lafollett, city manager of Nacogdoches about 145 miles northeast of Houston.

The shuttle had closed out experiments conducted on the mission, which was deemed a success by NASA. The shuttle did not visit the International Space Station this trip.

The next space shuttle mission was to have left on March 1 to carry a new segment to the space station, with astronaut Eileen Collins in command of the shuttle Atlantis.

(China Daily February 2, 2003)