MANILA, Philippines ? (UPDATE 3) Congress late Wednesday suspended its historic joint session to discuss Proclamation 1959 by President Gloria Macapagal-Arroyo declaring martial law in Maguindanao province.

The session officially started at 4:12 p.m. and was suspended at past 10:30 p.m. with both Senate President Juan Ponce Enrile and Speaker Prospero Nograles presiding. Present were 18 senators and a total of 192 congressmen.

The session will resume at 2 p.m. Thursday.

Palace officials led by Executive Secretary Eduardo Ermita explained the basis for the proclamation in a presentation before the plenary. Also present were Justice Secretary Agnes Devanadera, Interior and Local Government Secretary Ronaldo Puno and Philippine National Police Chief Jesus Versoza.

Defense Secretary Norberto Gonzales is in Singapore and will be back Thursday while Armed Forces of the Philippines Chief of Staff Victor Ibrado is due to arrive in Manila in the afternoon from China.

Lieutenant General Rodrigo Maclang was sent in to take their place.

Ermita said Gonzales was in an ?important mission? in Singapore in connection with the resumption of the talks between the government and the Moro Islamic Liberation Front.

Senators and congressmen started grilling Palace and security officials on the basis for the declaration of martial law in Maguindanao.

Ermita stressed that the issuance of Proclamation 1959 on the province was a ?faithful exercise? of President Gloria Macapagal-Arroyo?s ?prime duty to preserve and defend the constitution.?

Showing a slideshow of photos in the plenary, Police Inspector Andres Caro, Philippine National Police operation director, reiterated the details of the November 23 massacre in Maguindanao that prompted the government to place it under martial rule.

Senator Benigno ?Noynoy? Aquino III, the first interpellator, questioned the basis for Malacanang?s decision to declare martial law in the province, when it said earlier that it was not needed.

Interior Puno, meanwhile, replied that verified reports of Ampatuan supporters amassing themselves in Maguindanao necessitated greater control of the province.

Ermita said martial law was needed because ?the situation had to be controlled to account for perpetrators, allow prosecutors to do their job, and at the same time, be able to gather enough evidence.?

Questioned anew by Aquino about the President?s extraordinary powers during martial law, Justice Secretary Devanadera said a state of emergency was not sufficient since it merely empowers the President to call on the armed forces and the police to take control of a particular area and quell lawlessness.

Devanadera said martial law and the suspension of the writ of habeas corpus allows the President to address rebellion and invasion.

She said the reports of the Armed Forces of the Philippines showed that the Ampatuans were linked to the massing up of armed groups.

?Because of the report that those who were originally organizing, originally recruited to defend the public and the people, these are the same people who have now been transformed into a private army. They now follow not the rule of the Republic but their leaders, the Ampatuans,? Devanadera said.

Both chambers, voting jointly, can revoke the proclamation. Lawmakers have approved the rules of procedure governing the deliberations.

Based on the rules, each chamber is given 10 hours for the interpellation. Nograles said he expects the deliberations to finish in four session days.

Nograles earlier said discussions can run for five hours a day for four days ? December 9, 10, 14 and 15.

?The target is from 4 p.m. to 9 p.m. We can do this in four days,? he told reporters in a news conference.

Asked if he expects long debates, he said, ?It depends. When the lawmakers have become engrossed in discussions, we don?t know when to finish.?

But he stressed that each chamber will have to stick with the maximum 10-hour limit for the deliberations.

?There will be no other extraneous matters that will be taken up except the report. The only motion to be entertained is the motion to revoke after we close the question and answer portion,? he said.

He added that no motion to revoke would be entertained unless the discussions are through or when everybody is satisfied.

Congress will go on break starting December 18.

Congress only holds joint session during the State of the Nation Address and to act as national board of canvassers in a presidential election.

Three resolutions, signed by 34 congressmen, have been filed in the House of Representatives calling for the revocation of martial law in Maguindanao.