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 (search), an Al Qaeda linked terror group, was behind Sunday's attack. President Gloria Macapagal Arroyo (search) 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 (search) 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. He said the last major attack was Feb. 14, when Manila and two southern cities were hit by deadly bomb attacks.

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.

National Police Chief Arturo Lomibao has put the police on heightened alert after intelligence reports that terrorists may be targeting metropolitan Manila.

"We have elevated our vigilance," said Manila's police chief, Director Vidal Querol.

Metropolitan Manila is composed of Manila and outlying cities that comprise the capital region.

Querol said he has sent out more railway police with dogs, installed more closed-circuit TV cameras in malls and other public places, and set up checkpoints along approaches to the city.

In Indonesia, the president also warned Monday that terrorists could launch an attack in the mostly Muslim nation in the next two months, and ordered security forces to step up surveillance.

"We know the terrorists cells are still active, they are still hiding, recruiting, networking, trying to find new funding and even planning ... for another strike," Susilo Bambang Yudhoyono (search) said at a seminar in Jakarta.

He warned of possible attacks in September or October, calling them "special months for terrorism."

Yudhoyono did not elaborate, but the Al Qaeda-linked Southeast Asian terror group Jemaah Islamiyah (search) has been blamed for the 2002 bombings on Bali island, the 2003 J.W. Marriott hotel attack and the 2004 Australian Embassy blast that together killed 225. All occurred between August and October.

Abu Sayyaf, which is on U.S. and European lists of terrorist organizations, has been blamed for a number of other bombings. Philippine security officials say the group also has ties with the Jemaah Islamiyah network.

The south is the homeland of the country's Muslim minority and a decades-old Islamic separatist insurgency.