U.S. officials said they are pressing commercial shipping companies to adopt their own measures to defend their ships from pirate attacks.

Defense Undersecretary for Policy Michele Flournoy during testimony on Capitol Hill, (File)

In testimony before a Congressional committee Senate Armed Services Tuesday, the Defense Department's undersecretary for policy, Michele Flournoy, said security measures aboard ships are the single most effective response to pirates, who have grown increasingly active in the waters off Somalia.

She said 78 percent of unsuccessful pirate attacks were stopped after the ships' crews took action.

One option for ships to secure themselves is to hire private armed security teams. During Tuesday's hearing, some lawmakers pushed for the U.S. government to formally recommend the shipping industry use private security on its most vulnerable ships.

Acting U.S. Maritime Administrator James Caponiti said officials are looking at the issues involved and could make a recommendation on private security on ships within a relatively short time.

But Caponiti cautioned that the issue of private armed security is controversial and has been met with opposition from the U.S. shipping industry as well as the European Union. He said there is a need for rules to protect ships from liability, as well as a need to take into account that many ports prevent armed ships from entering.

Sailors stand on deck of the USS Bainbridge as it sails into Mombasa harbor, 16 Apr 2009

The Pentagon has rejected calls by several lawmakers to put U.S. military forces on board commercial vessels.

Flournoy said the U.S. military will continue to respond when U.S. flagged vessels are attacked, but that the Defense Department would be reluctant to provide military security for private shipping, except in extraordinary cases.

The United States, the European Union and a number of other nations have dispatched naval forces to the Gulf of Aden to respond to the increasing attacks by Somali pirates. U.S. officials have called for a coordinated international effort to fight piracy, including new strategies to prosecute and imprison pirates, track and freeze the assets of pirates, and secure the release of ships still held in the region.