VATICAN CITY -- Pope John Paul II expressed his sadness at the explosion of the space shuttle Columbia and asked for prayers for the seven astronauts who died in the accident.

The pope was informed of the tragedy shortly after news agencies reported Feb. 1 that the space shuttle had broken up on re-entering Earth's atmosphere over Texas. Aides said he received the news with "extreme sadness" and prayed for all those touched by the disaster.

Speaking to several thousand people at a noon blessing the following day, the pope expressed his spiritual closeness to the families and friends of those killed.

"The sad news of the tragic explosion of the U.S. space shuttle Columbia has stirred deep emotions in everyone. I ask everyone to pray for the victims, who died while fulfilling an international scientific mission," he said.

"At this time of difficult trial, I am spiritually close to the relatives, and I assure them of my prayers," he said.

Experts were investigating why the shuttle burst into flames and disintegrated on its way to a planned landing in Florida. Flying on the space ship with six U.S. crew members was Israel's first astronaut, a former fighter pilot and father of four.

Also on board was the first Indian-born woman astronaut, who became a naturalized citizen after immigrating to the United States.

In Jerusalem, Father Shawki Batarian, chancellor of the Latin Patriarchate, said Patriarch Michel Sabbah had made special mention of the seven astronauts in his daily prayer for all victims of accidents and violence.