MANILA, Philippines?Congress will hold a joint session on Tuesday to approve or revoke martial law in a southern province where 57 people were massacred last month, the Senate President Juan Ponce-Enrile said.

Members of the Senate and the House of Representatives will first study President Gloria Arroyo's report on the move that is expected to be submitted to Congress on Sunday, he said.

"We are waiting for the president's report," Enrile said on dzBB radio.

"The action of Congress now is (to decide) whether to reject it, if we are not convinced. Or if we are convinced, to allow it to last for 60 days as mandated by the constitution."

He said his counterpart in the lower chamber, House Speaker Prospero Nograles, had agreed to hold the joint session on Tuesday.

Arroyo declared martial law in Maguindanao province late Friday to quell what the government said was a rebellion led by a powerful Muslim clan, whose members have been accused of masterminding the massacre on November 23.

Her critics warned that the unpopular president could expand martial law to cover the entire country in a bid to hold on to power.

"I will not give an opinion or a judgment as of now. I am going to study the facts, because I do not know the facts that the president used when she decided to declare martial law," Enrile said.

Arroyo's declaration triggered fears in some sectors that the country may descend into dictatorship similar to the 20-year regime of Ferdinand Marcos.

Under martial law, Marcos used his troops to stifle dissent and jail thousands of activists. He was toppled in a bloodless popular revolt in 1986, and died three years later in exile in Hawaii.

The Constitution grants a president the power to declare martial law for 60 days in cases of invasion or rebellion.

Voting jointly, the congress by a simple majority may revoke the declaration, approve it, or extend it.