Philippine security authorities are on high alert a day after bombings in the south of the country. Officials are also warning that foreign terrorists may be planning attacks.

Police inspect damaged vehicles after bomb exploded last night in  southern port city of Zamboanga

Police suspect the local Muslim extremist group Abu Sayyaf in Wednesday's twin blasts in the southern city of Zamboanga.

Police are questioning at least three people about the blasts that injured at least 26 people.

National Security Adviser Norberto Gonzales warned Thursday that he had intelligence reports saying at least 10 suicide bombers from Indonesia were being sent to the Philippines. He said two could already be in Manila scouting possible targets.

He added the group is believed to be working with the Abu Sayyaf, which officials previously said is training militants from the regional terror network Jemaah Islamiya, or JI.

National police spokesman General Leopoldo Bataoil said police are not ruling out the participation of foreign terrorists in Wednesday's blasts.

"There were some reports in the past by intelligence groups of JI linking with our local terrorist groups like the Abu Sayyaf," he said. " But for now it is too early to say which particular group is involved. We will make comparisons with previous [bombing] incidents not only here in the local setting but also abroad."

Philippine officials have previously warned that some of Asia's most wanted terrorists, linked to deadly bombings in Bali and Jakarta, may be hiding in the southern island of Mindanao, which shares a porous maritime border with Indonesia. Authorities on Mindanao have captured several Indonesian JI suspects in recent years.

The southern Philippines experiences frequent violence by local militants and Muslim separatists. Since 2002, U.S. troops have held joint military training with Philippine soldiers in the region as part of anti-terrorism cooperation between the two countries.