MANILA, Philippines —(UPDATE 2) Hundreds of soldiers crept into a major lair of the Abu Sayyaf in a village in Basilan Wednesday night, to carry out what military officials described as a thorough and "intelligence-driven" combat operation against suspected terrorists.

When the daylong "hand-to-hand" gun-battle ended and the smoke cleared, 23 soldiers—two of them young officers belonging to the Army's elite group— were killed and 22 others were wounded in the biggest clash with the Abu Sayyaf so far.

A saddened military on Thursday could not remember suffering such heavy casualties following the carnage on July 20, 2007 when 14 Marines were killed—10 of them beheaded—during a fruitless rescue operation for kidnapped Italian priest Giancarlo Bossi.

Of the fatalities, 20 soldiers belonged to the Philippine Marines while the rest were from the Army, said AFP spokesperson Lieutenant Colonel Romeo Brawner Jr. in a press briefing at Camp Aguinaldo Thursday.

"It was a deliberate operation launched by the military targeting this camp, which is the heart of the Abu Sayyaf activities," said Brawner.

"We are saddened by our loss ... but it is an accepted fact that part of our duties would entail risk of being killed in action, death is a natural consequence of such operation," he added.

Army spokesperson Lieutenant Colonel Arnulfo Burgos Jr. identified the two junior Army officers as First Lieutenant Chester Barela of the Philippine Military Academy Class 2004 and First Lieutenant Dhel Jhun Evangelista (PMA Class 2006).

Corporal Renato Dindin, an Army enlisted personnel, also died in the combat operation.

Family and relatives of the three soldiers were informed of the sad news Wednesday afternoon, Burgos told the INQUIRER over the phone.

Barela, a member of the 4th Scout Ranger Company, and Evangelista of the 3rd Light Reaction Company, were among the first soldiers to enter the Abu Sayyaf lair in Barangay Silangkum in Tipo-Tipo town, according to Brawner.

"It was still dark when the firefight began. The two officers were equipped with night vision goggles so they were in that group who first launched the operation," he said, adding that soldiers fought with the Abu Sayyaf at very close range.

The first clash began at around 3:30 a.m. with initially 50 Abu Sayyaf fighters.

A bigger clash occurred two hours later or at around 5:30 a.m. and lasted for seven hours with at least 300 troops engaging roughly 150 Abu Sayyaf members.

Sporadic firefighting erupted until Wednesday evening in adjacent villages as Abu Sayyaf fighters clashed with the military's blockade forces, added Brawner.

The camp which the military overran on Wednesday was believed to have been headed by Abu Sayyaf commander Furuji Indama. Amateur members of the al-Qaida linked group were being trained in bomb-making in the said camp.

After the fierce fighting, troops recovered from the camp a "significant number" of improvised explosive devices apparently ready for use, according to reports reaching the general headquarters Thursday.

Despite suffering heavy casualties, Brawner said the operation was partly a success, as the military crippled the Abu Sayyaf's capability to launch further attacks.

"This is a big blow to their capability, especially to launch bombings, because we have deprived them of improvised explosive devices," he told reporters.

He added, "however, we are not yet certain that they would not launch other attacks later on."

Government troops conducting clearing operations in the area Thursday have recovered 21 bodies out of the roughly 30-40 Abu Sayyaf members killed in the biggest encounter since July 2007, said Burgos.

When asked if AFP Chief of Staff General Victor Ibrado has given any directive in relation to Wednesday's clash, Brawner said that the military commander is relying on Western Mindanao Command Chief Major General Ben Dolorfino.

Follow-up operations for the remaining Abu Sayyaf bandits are ongoing, Brawner said.