Unknown assailants gunned down a Philippine reporter Thursday, the second journalist killed in the country this week. The attacks are part of a pattern that makes the Philippines one of the most dangerous places in the world to be a journalist.

Arnel Manalo was ambushed and fatally shot three times just minutes after he dropped his two children off at school Thursday morning. Mr. Manalo was a newspaper and radio reporter in Batangas Province, about 100 kilometers south of Manila.

Police have launched an investigation into the slaying, but have offered no possible motives for the attack.

Mr. Manalo's murder comes just five days after another journalist, Roger Mariano, was shot to death by unidentified gunmen using machine guns. Mr. Mariano was a well-known radio broadcaster in the north of the country, and a vocal critic of police misconduct.

Already this year four reporters have been killed in the Philippines. Last year seven journalists were murdered, the most in nearly two decades. The violence has prompted allegations that corrupt officials in rural provinces are trying to suppress public scrutiny of their actions.

The Southeast Asian Press Alliance, a media watchdog group based in Indonesia, says most of the murdered Filipino journalists were investigating official corruption.

The Alliance's Kulachada Chaipitat says few if any of the killers have been caught or successfully prosecuted. "The government is not doing enough, there has been no action, no effort to bring those who are responsible for the killing to justice," she said.

The Philippines is well known for its free and robust press. It is also known for the dangers involved in the profession. Nearly 50 journalists have been killed there since 1986.

Ms. Chaipitat said this record challenges Philippine government assurances that it is protecting those in the news media. "Press freedom is healthy, but for the safety of journalists it's worse than any other country in this region," she said.

Other journalist organizations have called the Philippines one of the most dangerous places in the world to practice journalism.

Opposition leaders in the Senate are calling for an investigation into the murder of Mr. Mariano, and into alleged efforts to muzzle the Philippine press.