WASHINGTON ( CNN ) -- A U.S. destroyer has entered Somali territorial waters in pursuit of a Japanese-owned ship loaded with benzene that was hijacked by pirates over the weekend , military officials said Monday . The destroyer USS Porter , shown in 2006 , sank pirate skiffs tied to the stern of the hijacked vessel . The guided-missile destroyer USS Arleigh Burke entered Somali waters with the permission of the troubled transitional government in Mogadishu , U.S. officials said . In recent years , warships have stayed outside the 12-mile limit when chasing pirates . The ongoing operation was confirmed to CNN by two military officials familiar with the details . Gunmen aboard two skiffs hijacked the Panamanian-flagged Golden Mori off the Socotra archipelago , near the Horn of Africa , said Andrew Mwangura , a spokesman for Kenya 's Seafarers ' Assistance Programme . The Golden Mori radioed for help Sunday night . The Burke 's sister ship , the USS Porter , opened fire and sank the pirate skiffs tied to its stern before the Burke took over shadowing the hijacked vessel . When the shots were fired , it was not known the ship was filled with highly flammable benzene . U.S. military officials indicate there is a great deal of concern about the cargo because it is so sensitive . Benzene , which U.S. authorities have declared a known human carcinogen , is used as a solvent and to make plastics and synthetic fabrics . U.S. and NATO warships have been patrolling off the Horn of Africa for several years in an effort to crack down on piracy off Somalia , where a U.N.-backed transitional government is struggling to restore order after 15 years of near-anarchy . In June , the destroyer USS Carter Hall fired warning shots in an attempt to stop a hijacked Danish cargo ship off Somalia , but the American vessel had to turn away when the pirated ship entered Somali waters . In May , a U.S. Navy advisory warned merchant ships to stay at least 200 miles off the Somali coast . But the U.S. Maritime Administration said pirates sometimes issue false distress calls to lure ships closer to shore . The pirates are often armed with automatic rifles and shoulder-fired rockets , according to a recent warning from the agency . `` To date , vessels that increase speed and take evasive maneuvers avoid boarding , while those that slow down are boarded , taken to the Somali coastline and released after successful ransom payment , often after protracted negotiations of as much as 11 weeks , '' it advised . The agency issued a new warning to sailors in the Gulf of Aden , between Somalia and Yemen , after Sunday 's hijacking was reported . E-mail to a friend .
Sources : U.S. destroyer has entered Somali territorial waters to pursue ship . Score: 6 ; benzene is highly flammable . U.S. destroyer working with permission of Somalia government .