British lawmakers are urging the government to clearly define when lethal force can legally be used against pirates.

The request is part of a report released Thursday by parliament's foreign affairs committee, which welcomed the government's decision last year to permit armed guards on British ships in dangerous waters.

The committee says captains still need specific instructions on what they can do if threatened by pirates.

Britain says a limited number of its ships have been attacked but, piracy continues to threaten the country's economy through its banking, insurance and shipping industries.

The report says Somali pirates have been paid more than $300 million over the past four years, but little is known about where the extorted money ends up.

The legislators say multi-national naval operations have had limited impact on piracy.

The report says even when pirates are detained, about 90 percent are released without being charged.

The committee says the government should consider trying pirates captured on British vessels in a national court unless they are prosecuted by another country.

Britain will convene an international conference in London next month on the threat of piracy off the coast of Somalia, including in the Gulf of Aden, the Arabian Sea and Indian Ocean.