Jakarta/Bangkok: Security forces across Asia were on alert on Friday ahead of the Christmas and New Year holidays, as police in Australia and Indonesia said they had foiled bomb plots and Malaysian security forces arrested suspected militants.

Australian police said they had prevented attacks on prominent sites in Melbourne on Christmas Day that authorities described as "an imminent terrorist event" inspired by Islamic State.

The announcement came after an attack in Berlin in which a Tunisian suspect smashed through a Christmas market in a truck on Monday, killing 12 people.

In Indonesia, where Islamic State's first attack in Southeast Asia killed four people in Jakarta in January, at least 14 people were being interrogated over suspected suicide bomb plots targeting the presidential palace in Jakarta and another undisclosed location, police said.

Anti-terrorism police killed three suspects in a gunfight on Wednesday on the outskirts of the capital, Jakarta.

Indonesia, the world's largest Muslim-majority country, would deploy 85,000 police and 15,000 military staff for the Christmas and New Year period, police said.

Moderate Indonesian Muslim groups were helping authorities secure Christmas celebrations amid heightened religious tension after the Christian governor of Jakarta, Basuki Tjahaja Purnama, went on trial on a charge of blasphemy against Islam, which he denies.

Hardline group Islamic Defenders Front swept into shopping centres in the city of Surabaya, in East Java, last week to make sure Muslim staff were not forced by employers to wear Santa hats or other Christmas gear.

In West Java, a group stopped a Christmas event as it was being held in a public building rather than in a church.

In Jakarta, about 300 volunteers from Nahdlatul Ulama, Indonesia's biggest moderate Muslim group, will join police in overseeing security.

"The focus is against terrorism, especially in Jakarta and Bali, because these are the traditional targets," Indonesia police chief Tito Karnavian told reporters.

The largely Hindu island of Bali, famed for its temples and beaches, suffered Indonesia's most serious militant attack, in 2002, when 202 people were killed, most of them foreigners, by bombs at a bar.

WARNINGS, PATROLS

Police in Muslim-majority Malaysia, where Islamic State claimed responsibility for a grenade attack on a bar on the outskirts of Kuala Lumpur in June, said this week they had arrested seven people for suspected links to the militant group.

Police will monitor transport hubs, entertainment centres and tourist spots.

"We try not to have too much physical presence in public and focus more on prevention," deputy home minister Nur Jazlan Mohamed said. "People should feel free to enjoy their holidays."

The U.S. embassy in India warned this week of an increased threat to places frequented by foreigners, and cited media reports indicating Islamic State's desire to launch attacks in the country.

In mostly Muslim Bangladesh, where a militant group killed 22 people, most of them foreigners, at a Dhaka cafe in July, police would be patrolling near churches, an officer said.

Mostly Buddhist Thailand plans to have more than 100,000 police on patrol until mid-January, police said, adding it was an increase from last year, without giving details.

Thai deputy national police spokesman Kissana Phathancharoen said no intelligence pointed to a possible attack but "we will not let our guard down".

Multi-ethnic Singapore, a major commercial, banking and travel hub that is home to many Western expatriates, will deploy police at tourist and shopping areas. Police said bags may be checked.

A spokesman for the Roman Catholic Archdiocese of Singapore said its churches had trained some members to watch out for people looking suspicious. Central St Andrew's Cathedral has installed more CCTV cameras and was doubling security staff.