File: A Maersk cargo ship like the one pirates attempted to hijack for a second time off Somalia.
Mar. 3: A Somali pirate boat is seen in the Gulf of Aden off the coast of Somalia.
The U.S. Navy ordered its ships to the scene of a hijacking off the coast of Somalia Wednesday after pirates commandeered a U.S.-flagged cargo ship crewed by 20 U.S. citizens.
Officials would not say how many Navy ships are on the scene nor would it confirm the nationality of the crew members, but sources told FOX News the Danish-owned ship is operated by U.S. shipping company, Maersk Line Limited.
Pentagon Spokesman Bryan Whitman said he has "no information to suggest the 20 crew members of the Maersk Alabama have been harmed by the pirates."
The Department of Defense has taken the lead on information-gathering. Whitman declined to comment when asked if military action would be taken.
Press Secretary Robert Gibbs said the White House is "closely monitoring the apparent hijacking of the U.S.-flagged ship in the Indian Ocean and assessing a course of action to resolve this situation."
"Our top priority is the personal safety of the crew members on board," Gibbs said in a written statement.
The 17,000-ton Maersk Alabama was carrying emergency relief to Mombasa, Kenya, at the time it was hijacked, said Peter Beck-Bang, spokesman for the Copenhagen-based container shipping group A.P. Moller-Maersk. A Kenya-based diplomat identified the crew as American, but Navy Spokesman Lt. Nathan Christensen declined to release details until family members of the crew are notified.
Just last week, A. P. Moller-Mærsk Group sold eight containerships to Maersk Line Limited to be run under a U.S. flag. The U.S. company also recently replaced eight older units flying U.S. flags, including the Maersk Alabama.
Flying under a U.S. flag means the ships are bound by U.S. law maritime regulations and can travel directly from U.S. port to U.S. port.
Christensen said the attack happened in the early hours of the morning, about 280 miles northeast of Eyl, a town in the northern Puntland region of Somalia. Andrew Mwangura of the East African Seafarers' Assistance Program said the ship was taken about 400 miles from the Somali capital, Mogadishu.
Just a day earlier, the Navy's 5th fleet warned "merchant mariners should be increasingly vigilant" when operating off the coast of Somalia.
"The area the ship was taken in, is not where the focus of our ships has been," Christensen told The Associated Press in a phone call from the 5th Fleet's Mideast headquarters in Bahrain.
"The area we're patrolling is more than a million miles in size. Our ships cannot be everywhere at every time," Christensen said.
Maersk does business with the U.S. Department of Defense, but Christensen said the vessel was not working under a Pentagon contract when hijacked.
"Our initial concern is to ensure proper support of the crew and assistance to their families," Maersk said in a statement.
The vessel is the sixth to be seized within a week and the first with an all-American crew.
At least 12 of the Americans aboard the Maersk Alabama are members of the Seafarers International Union, spokesman Jordan Biscardo said. The union is trying to get as much information on the situation as it can, he said.
"It goes without saying we're deeply concerned and we're closely monitoring the story," Biscardo said.
Biscardo would not immediately release the names of the union members aboard the vessel. The Seafarers International Union represents unlicensed United States merchant mariners sailing aboard U.S.-flag vessels.
FOX News' Justin Fishel and The Associated Press contributed to this report.