Pope John Paul II has approved further research to help solve the mystery surrounding the Shroud of Turin, the linen that many believe was Jesus Christ's burial cloth.

Journeying to Turin, John Paul on Sunday knelt to pray before the shroud, which is now on display in Turin's cathedral."The shroud is a challenge to intelligence," John Paul said. He asked scientists to study it "without preconceived positions" and with "scientific methodology and the sensibility of the faithful."

In 1988, scientists concluded after testing scraps of the 14-foot-long, 31/2-foot-wide linen shroud that it dated back to the 13th or 14th century. However, they admitted they couldn't explain how the image on the shroud - a man with wounds similar to those suffered by the crucified Christ - was formed.

"(The church) entrusts to scientists the tasks of continuing to investigate, to reach adequate answers," said John Paul, who became the longest-serving pope of this century on Sunday by surpassing the 19 years, seven months and seven days of Pius XII, who died in 1958.

While still bishop of Krakow, Poland, John Paul came here in 1978 to see the shroud during its last previous public viewing. He saw the shroud again in 1980.

After the current display ends on June 14, the shroud will next be shown to the public during Holy Year celebrations in 2000, and there are indications more tests might be allowed after that.

The pope spoke of the cloth's "mysterious fascination," and the "preciousness of this image, which all see and no one, for now, can explain."

John Paul seemed to suggest that, whatever its origin, the shroud will remain important to the church because it is "the icon of the suffering of the innocent of all times."