Updated

MANILA, Philippines -- The United States and Australia warned of possible terrorist attacks in Manila and the southern Philippines, sparking a security alarm in the bustling capital Wednesday with additional deployments of police patrols and intelligence agents.

Although the U.S. and Australia have previously issued similar security alerts for the volatile southern Philippines, where Muslim rebels and al-Qaida militants are active, both specifically mentioned Manila as a possible target in their latest travel advisories.

Australia, citing unspecified but reliable reports, said an attack in the capital may be "imminent."

Philippine Defense Secretary Voltaire Gazmin said Wednesday that the military and police have not monitored any specific threat but that the government is taking no chances.

The Western countries, along with Britain, warned their citizens visiting the Philippines to stay away from shopping malls, convention centers and places frequented by foreigners. The warnings did not identify the source of the threat or release other details.

"Reliable reports indicate that terrorist attacks may be imminent in Manila," said Australia's advisory posted on a government website.

U.S. and Australian embassy officials contacted by The Associated Press did not elaborate on their governments' advisories.

British Embassy Deputy Chief of Mission Colin Crorkin said his country's assessment of the high risks of terrorist strikes in the Philippines had not changed but added that his government recently included additional possible targets such as airports, malls and places of worship.

A Philippine official said the warnings may have come from a confidential terrorist threat assessment report by Western security officials indicating that unspecified Muslim extremists may attack a popular Manila mall, a trade center and political figures, including Manila-based diplomats. The official, who monitors security threats, spoke on condition of anonymity for lack of authority to talk to the press.

Gazmin told the AP that the government sent intelligence agents to verify the threat. Authorities also plan to ask the U.S., Australian and British embassies to provide more details.

"We are taking this seriously, and we know that this is creating apprehension," Gazmin said. "We have deployed intelligence agents but they have not come back with anything specific."

He said he discussed with the military chief of staff, Lt. Gen. Ricardo David, the possible deployment of marines in shopping malls and other public areas. However, Gazmin was reluctant to immediately take that step because it has been criticized in the past by leftist lawmakers.

The Philippines, including its capital, has been hit by deadly terrorist attacks in the past.

Despite years of battle setbacks, Muslim militants, including those from the Al Qaeda-linked Abu Sayyaf, have continued to plot attacks, at times collaborating with Indonesian militants belonging to the Jemaah Islamiyah terrorist network, according to the military.

Abu Sayyaf militants were blamed for the bombing of an inter-island ferry in Manila Bay in 2004, setting off an inferno that killed 116 people in Southeast Asia's second-worst terrorist strike.

The militants also claimed responsibility for Feb. 14, 2005 bombings of a bus in Manila's Makati financial district and two other southern towns that killed eight people and wounded more than 100 others.