Another U.S.-flagged cargo ship was attacked by pirates Tuesday off the coast of Somalia, though U.S. Navy officials refused to speculate whether the brazen attack was related to pirates’ promises of retaliation.

Tuesday’s attack on the Liberty Sun, with its roughly 20-member crew of U.S. citizens, included pirates shooting rocket-propelled grenades and automatic weapons in a failed attempt to take over the ship, officials said. The ship had been headed toward Mombasa, Kenya, to deliver food aid, said Lt. Stephanie Murdock, a spokeswoman with U.S. Naval Forces Central Command/5th Fleet.

The incident comes on the heels of the Maersk Alabama incident, which ended when Navy SEALs aboard the USS Bainbridge shot and killed three pirates who held the Alabama’s captain, Richard Phillips, on a lifeboat for five days.

Murdock would not say whether the U.S. Navy or coalition forces have altered their mission as a result of the attacks on two U.S.-flagged vessels or on the pirates’ threat to seek vengeance for five pirates who have been killed by U.S. and French forces in two recent at-sea hostage rescues.

But maritime analysts and military experts said the most recent incidents showed that a sea-based effort in fighting the piracy is not effective enough.

Jim Gavrilis, an international affairs fellow at the Council on Foreign Relations and retired U.S. Special Forces lieutenant colonel, said there are also limits to what the military can do on land.

"There would be short term military gains, eliminating some pirates, and possibly slowing down some of the piracy for a while," he said.

But, he warned, military strikes alone won’t solve the problem.

"It is too profitable, there are little alternatives for business, and there is no government to keep criminal organizations in check," said Gavrilis, adding that without a functioning government, piracy will continue to be a problem.

"Military operations will not change the environment that allows pirates to flourish. The more limited the military operations are, the more successful they will probably be. Longer duration operations with broad missions will likely get bogged down," he said.

The recent hijacking incidents show "that no sea space anywhere remotely near Somalia is safe. And that the Somali pirates are by now very accomplished seafarers," said Jim Wilson, Middle East correspondent for Fairplay International Shipping Weekly and with Lloyd’s Register-Fairplay, a global provider of maritime information to the shipping industry.

The Liberty Sun was approached by suspected pirates on two small boats, officials said.

"The pirates were not successful in their attempt to board the vessel and the Liberty Sun proceeded to perform evasive maneuvers," a Navy spokeswoman said.

Crewmember Thomas Urbik sent his mother an e-mail detailing some of the attack, according to The Associated Press.

"We are under attack by pirates, we are being hit by rockets. Also bullets," the AP quoted Urbik’s e-mail. "We are barricaded in the engine room and so far no one is hurt. [A] rocket penetrated the bulkhead but the hole is small. Small fire, too, but put out."

The number of ships and crew held by Somali pirates varies, depending on the source. The NATO anti-piracy mission reports 16 ships are being held for ransom, while the International Maritime Bureau says 19 ships and some 300 crewmembers are being held.

The U.S. Navy says that 23 hijackings have occurred so far this year — well ahead of 2008’s pace, when a record 40 hijackings were reported.

The Navy spearheads Combined Task Force 151, a multinational effort to prevent pirates from attacking merchant ships in the Gulf of Aden. The European Union also has established an anti-piracy effort in the region, and nations like Russia, China and Japan have sent ships to escort convoys of ships through pirate-infested waters.

Responsibility for the piracy problem is split between units in the Gulf of Aden and units on land. The task force falls under U.S. Central Command, which oversees hot spots such as Iraq and Afghanistan, but not Africa. While U.S. Central Command is responsible for any maritime operations in that region, U.S. Africa Command would head up any that are land-based.

"We have not been directed to conduct any operations in Somalia," spokesman Vince Crawley said.

Somalia instead sits in the domain of Africa Command — specifically, its subordinate command, the Combined Joint Task Force–Horn of Africa.

Piracy, spawned in the lawlessness of Somalia, has not changed the CJTF-HOA’s core mission, said spokesman Air Force Capt. Matthew Stines.

That mission focuses on civil-military operations, military-to-military training and improving conditions for foreign investment, Stines said in an e-mail.

"Our overarching goal with these programs is to create an environment that counters the ideological support of extremism," he wrote.

The efforts thus have been handled as a criminal problem, not as a military one.

"The U.S. [has], in relation to Somali piracy, been very reluctant to intervene with force when ships, flags and crews of other nations have been involved," Wilson said. "They have tended to let the owner take the lead. With the U.S. crew/flag, they have opted to use deadly force rather than pay a ransom or give safe passage to the pirates."

But, he said, "I sense that there is quite a lot of political indignation that a U.S. vessel has been attacked. I can’t really tell what, or if, this will translate into political or direct action in relation to the long-term Somali piracy problem, but the potential is there."

Stars and Stripes’ John Vandiver contributed to this report.

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