Police installed more closed-circuit cameras in Manila malls, sent out guards with dogs and set up checkpoints on roads Monday as a senior official warned of a possible major attack in the capital following a ferry bombing that injured 30 people.

The military said an initial investigation concluded that Abu Sayyaf, an al-Qaida linked terror group, was behind Sunday’s attack. President Gloria Macapagal Arroyo promised to hunt down “and cripple, if not decimate,” those responsible.

The ferry was docked at a wharf in the southern Philippines and preparing to depart with more than 300 passengers when the bomb, hidden in a cardboard box filled with old clothes, went off.

“Terrorist attacks … normally come in cycles, and it’s unfortunate that we are in that cycle again,” National Security Adviser Norberto Gonzales said on television. “Sometime this month and next month, we are anticipating a major terrorist attack and most likely in Manila.”

Gonzales cited a pattern where terrorists carry out attacks every six months.

The reported entry of 10 suicide bombers from Indonesia, an influx of foreign funds for a terrorist action, and the discovery of 1,322 pounds of explosives this year point to another attack, he said.