NAIROBI, Kenya – A U.S. Navy destroyer helped sailors who regained control of their vessel Tuesday in a deadly battle with pirates after the North Korean-flagged ship was hijacked in the piracy-plagued waters off Somalia, the American military said.

The Navy also confirmed that other American warships sank two pirate ships late Sunday after answering a distress call from a hijacked Japanese chemical tanker and said U.S. ships were still monitoring that vessel.

In Tuesday’s incident, a helicopter flew from the destroyer USS James E. Williams to investigate a phoned-in tip of a hijacked ship and demanded by radio that the pirates give up their weapons, the military said in a statement.

The crew of the Dai Hong Dan then overwhelmed the hijackers, leaving two pirates dead, according to preliminary reports, and five captured, the military said.

Three seriously injured crew members were taken aboard the Williams, the statement said. The captured pirates remained on the Dai Hong Dan, which the crew was returning to the port of Mogadishu, Somalia’s capital.

“When we get a distress call, we help,” said Cmdr. Lydia Robertson, spokeswoman for the U.S. 5th Fleet, told The Associated Press by telephone from Manama, Bahrain.

Defense Department spokesman Geoff Morrell said the incident didn’t indicate the U.S. military was taking a more aggressive stance toward pirates off Somalia, but added that piracy in the Horn of Africa region is a concern because “you’re talking about an area that has seen greater terrorist involvement.”

Morrell said it was logical that the military would want to know “what is being transported on the high seas and who is out there operating and if they have nothing but the best intentions in mind.”

A Navy spokeswoman, Lt. Jessica Gandy, said later that the American destroyer had not been shadowing the North Korean ship. She said it was not known what its cargo was.

Andrew Mwangura, program coordinator of the Seafarers Assistance Program, said an estimated 22 crew members were aboard the North Korea-flagged ship that gunmen seized late Monday in Somali waters. His group independently monitors piracy in the region. Workers at the Mogadishu port said the vessel had delivered a load of sugar from India.

An international watchdog reported this month that pirate attacks worldwide jumped 14 percent in the first nine months of 2007, with the biggest increases in the poorly policed waters of Somalia and Nigeria.

Reported attacks in Somali waters rose to 26, up from eight a year earlier, the London-based International Maritime Bureau said through its piracy reporting center in Kuala Lumpur, Malaysia.

The U.S. Navy said that warships in a coalition monitoring the waters near Somalia were following the hijacked Japanese tanker Golden Nori and that four other vessels were still controlled by pirates near Somalia.

Robertson, the 5th Fleet spokesman, said coalition ships fired on and sank two pirate skiffs tied to the Golden Nori on Sunday night. A Navy photo showed one of the skiffs burning after being hit by a gun aboard the USS Porter, a guided-missile destroyer.

Robertson could not confirm CNN reports Tuesday that the Japanese tanker was filled with highly flammable benzene. But she said, “we were aware of what was on the (Golden Nori) ship when we fired.”

CNN said the USS Arleigh Burke, another guided-missile destroyer, was also involved in the operation and had entered Somali waters with the approval of the government.

Associated Press writer Lily Hindy in New York contributed to this report