Tens of thousands of police officers will guard churches across the world's most populous Muslim country over the Christmas period, amid concerns that al-Qaida-linked militants could carry out attacks, police said Monday. The regional terror network Jemaah Islamiyah has been blamed for annual strikes in Indonesia since 2000, when a series of coordinated bombings killed 19 people on Christmas Eve. An attack on a Christian market last New Year's Eve killed seven. More than 18,000 police will be posted at thousands of churches and religious sites in the capital, Jakarta, said police spokesman Col. Ketut Untung Yoga. Security was also increased in Poso, on Sulawesi island, which has been the flashpoint of violence between Christians and Muslims in recent years and has seen a surge in tensions since the execution of three Christian militants in September.