Japan will dispatch two destroyers to waters off Somalia for a mission protecting its commercial vessels against pirates, joining a growing number of countries patrolling those waters, an official said Wednesday.

The government will also send a fact-finding mission to the region ahead of the deployment of the 4,650-ton Sazanami and the 4,550-ton Samidare, a spokeswoman for the Defense Ministry said on condition of anonymity, citing department policy. Each ship has a helicopter aboard.

Japan previously has said it will join the fight against piracy, but the details confirmed by the ministry official Wednesday were the first mention of how many ships would be sent.

Somalia is located along the Gulf of Aden, one of the world's busiest waterways, where pirates made more 100 attacks on ships last year and took away millions of dollars in ransom.

Somali waters are now patrolled by more than a dozen warships from countries including Britain, France, Germany, Iran, the United States and China. South Korea has also ordered warships sent to the region to protect its vessels and crews from pirates.

Tokyo has said its ships will be sent only to protect Japanese commercial vessels — though the government says none have thus far been hijacked. Pirates have fired at three Japanese vessels. No one was injured.

Japan has yet to say when its ships will depart, but media reports say the dispatch could come as early as March.

Opposition lawmakers have criticized the plans, saying it could draw the country into military operations prohibited by its pacifist constitution.

Japan's post-World War II charter limits its military to conducting defensive operations. However, its navy has been increasingly operating far away from the country's shores. It began a refueling mission in the Indian Ocean since 2001 to support U.S.-led forces in Afghanistan.

The government has argued that the battle against piracy is more a crime-fighting operation than a military one. The defense ministry spokeswoman said Wednesday that Japanese coast guard officials vested with rights to arrest and investigate suspected pirates will be on board.

Somalia, a nation of about 8 million people, has not had a functioning government since warlords overthrew a dictator in 1991 and then turned on each other. Its lawless coastline is a haven for pirates.

The U.N. Security Council has authorized countries to enter Somalia's territorial waters, with advance notice, and use "all necessary means" to stop piracy and armed robbery at sea.