Mr Obama also praised the military's successful efforts to rescue merchant Capt Richard Phillips, who had been held hostage there for several days by pirates.

'His safety has been our principle concern,' the president said in his first remarks in public on the five-day standoff that ended on Sunday with Capt Phillips' release.

Mr Obama spoke at an unrelated Transportation Department event involving the economic stimulus initiative.

In a sharp warning to increasingly brazen pirates operating off the coast of lawless Somalia, Mr Obama said: 'I want to be very clear that we are resolved to halt the rise of piracy in that region and to achieve that goal, we're going to have to continue to work with our partners to prevent future attacks.'

'We have to continue to be prepared to confront them when they arise, and we have to ensure that those who commit acts of piracy are held accountable for their crimes,' the president said.

One day after Navy Seal snipers killed the three pirates holding Capt Phillips, Mr Obama said he knew the cargo ship captain's safe return was a 'welcome relief' to the man's family and crew.

'I'm very proud of the efforts of the US military and many other departments and agencies that worked tirelessly to resolve this situation,' Mr Obama said.

'I share our nation's admiration for Captain Phillips' courage and leadership, selfless concern for his crew.'

Earlier, Pentagon spokesman Bryan Whiteman told reporters the successful end to the standoff could discourage future attacks on commercial ships sailing the Indian Ocean.

But some penalties previously taken in such situations failed to deter lawlessness on the high seas, he acknowledged.

Mr Whitman also said that the shootings could make pirates less inclined to attack ships. -- AP

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