Malacanang condemned on Tuesday the terrorist attack in Basilan, saying the incident constitutes a war crime.

"We condemn in the strongest possible term the latest terrorist attack in Basilan perpetrated in violation of our laws," said Presidential Spokesperson Harry Roque in a press briefing.

At least 11 people were killed and eight were injured in the explosion that rocked a military checkpoint in Lamitan City early Tuesday.

Those killed include a soldier, five militiamen and five civilians, including the driver of the van.

Roque said the attack could be considered a war crime, noting that under Republic Act No. 9851 or the International Humanitarian Law Act of 2009.

"We note that even in times of war, the attack constitutes a war crime because it constitutes an indiscriminate attack which is prohibited by Article 4C-1 Attacks on Civilian, by R.A. 9851, IHL Act of 2009," he said.

He said Basilan is an area with a non-international armed conflict.

"So under the IHL, you must limit your attacks pursuant to military objectives; you must limit it to military targets, and you must avoid protected individuals including civilians," he said.

According to the military, the Abu Sayyaf Group was allegedly behind the attack.

Asked how the incident would fit in the offer of President Rodrigo Duterte to the ASG to talk peace, Roque said, "we do not know who's behind it yet. They're still investigating."

He also said that the offer of Duterte to the ASG was on an individual basis.

"I clarified that the president, of course, is enjoining individual fighters of the ASG to surrender, because they can still be accommodated as surrenderees in the same way that we are accepting surrenderees from the NPA (New People's Army) and the MILF (Moro Islamic Liberation Front)," he said. Celerina Monte/DMS