Britain, Canada and Australia on Saturday joined the US in issuing a security alert for their citizens in the Philippines after the US embassy warned of a threat against Americans in the capital.
The warnings urged Westerners in Manila to be on alert amid fears they could get caught up in an attempted attack against Americans, following the US embassy warning issued Friday.
"Any attack could be indiscriminate and we advise British nationals to exercise particular caution and extra vigilance in places frequented by expatriates and foreign nationals," the British foreign office alert said.
The Canadian foreign affairs office said "continuing reports suggest that there is an ongoing terrorist threat to Westerners and Western interests in the Philippines".
On Friday, the US embassy warned that an unspecified threat against Americans in the capital had been detected by "reliable security forces".
"This threat remains in effect until October 10, 2012," the advisory said.
The US embassy would not elaborate on the danger.
Both military and police spokesmen said the threat warning did not originate from them, adding they were unaware of any specific plot against Americans, but also said coordination had been increased with the embassy to tighten security and monitor possible threat groups.
President Benigno Aquino's spokeswoman Abigail Valte said the police presence had been heightened in the capital to safeguard not only Americans but also ordinary citizens.
The US government issued an alert in November 2010 that warned of an attack in Manila, particularly areas frequented by foreigners, which also prompted similar travel advisories from Britain, Australia, Canada, New Zealand and France.
The attack never materialised and Aquino subsequently criticised the Western allies for damaging his country's tourism prospects.
The United States has a general warning about the risks of travel in the Philippines, a former US colony that has for decades battled Islamic separatist rebels and more hardline Muslim militants in the far south of the country.
The Abu Sayyaf, a small band of Muslim militants that authorities say was set up in the early 1990s with funds from the Al-Qaeda network, has kidnapped and killed Americans in the southern Mindanao region in recent years.
About 600 US troops have been rotating through the southern Philippines for a decade to help train local troops in hunting the Abu Sayyaf. However the Americans are barred from taking part in combat.