SEOUL, South Korea (AP) — Police raided the house of a South Korean Christian activist and were questioning him for a second day Saturday after he returned home from an illegal trip to North Korea, an official said.

During his stay in the reclusive communist nation, the Rev. Han Sang-ryol accused his home country of sinking its own warship in March and raising tensions on the peninsula.

He was detained Friday upon crossing the truce village of Panmunjom along the border separating the Koreas, a police official said. He asked not to be identified because he was not authorized to speak to the media.

The official said prosecutors could seek an arrest warrant as early as Sunday and a court could decide Monday whether to issue it. It could accuse Han of violating tough national security laws the South maintains because it believes the North poses a threat despite a decade of reconciliation.

The security laws prohibit South Koreans from joining pro-North Korean organizations or having unauthorized contact with the North. They also ban citizens from supporting or praising the North. A separate law also bars its citizens from visiting North Korea without government permission.

Han could face up to seven years in prison if convicted, police said.

During his trip, Han blamed Seoul for the sinking the Cheonan warship in March and accused South Korean President Lee Myung-bak of raising tension with North Korea by discarding rapprochement accords and staging military exercises with the United States.

In May, an international team of investigators concluded that the North sank the ship with a torpedo, killing 46 South Korean sailors. North Korea denied involvement, and has issued a series of threats to South Korea over the military drills.