"Too much blood is still being shed on the earth! Too much violence and too many conflicts trouble the peaceful coexistence of nations!" the pope said in his traditional midnight mass at the St Peter's Basilica in the Vatican.

The plea came as mayhem and bloodshed rocked Iraq and security around the world was stepped up to high alert against Christmas terror attacks.

Baghdad's Sheraton Hotel, which houses mostly foreign journalists and contractors, was targetted in a wave of mortar attacks Thursday morning after four US soldiers and six Iraqi were killed in a series of bomb blasts on Wednesday.

Tensions were heightened after France cancelled six flights between Paris and Los Angeles Wednesday due to fears of a threat to the United States from passenger jets following a warning from the US embassy.

Security around the United States embassy in London was also beefed up due to the fears of a threat to US interests during the Christian holiday.

Tight security was in place as Indonesian Christians flocked to churches across the world's largest Muslim-populated state to solemnly celebrate Christmas.

There was no report of violence by noon, including in Central Sulawesi's restive Poso district and in Ambon and Maluku, where sectarian violence between Muslims and Christians has continued intermittently despite state-sponsored peace pacts.

On Wednesday evening, churches were packed for services as almost 166,000 officers backed by 1,000 soldiers were reported to be deployed across Indonesia for the festivities -- more than 22,000 of them in Jakarta alone.

Jakarta police and the US embassy have warned of a high risk of seasonal terror attacks from the al-Qaeda-linked Jemaah Islamiyah (JI).

Security was also increased in two other Asian countries where Christians live alongside Muslims and other religion followers -- the Philippines and Sri Lanka.

Philippine National Security Adviser Roilo Golez said military and police forces were on tight alert amid the Christmas season, guarding bus terminals and sea and airports to prevent a repeat of a series of bombings that killed about 20 people in December 2000, officials said Thursday.

Golez said the alert was imposed even before the United States its alert level for possible terror attacks from 'elevated' to 'high' at the weekend, prompting tighter security and even some cancelled flights overseas.

"We have a security alert but no specific threat," Golez said.

In Sri Lanka, elite commando units were posted outside the home and offices of a leading Roman Catholic businessman implicated in the death of Buddhist monk. They were also guarding other Christian symbols in Colombo.

In the communist nations of China and Vietnam, however, Christmas Day was being embraced on a more optimistic note.