The US has played down a statement by Somalia's prime minister that he had secured agreement for the US navy to patrol Somali waters to fight piracy.
International monitors have recorded 41 attacks in the past year
Prime Minister Ali Mohammed Ghedi had told ministers he agreed the deal on Sunday with the US ambassador to Kenya.
But the US State Department said discussions had taken place about possible co-operation to fight piracy, but there had been no deal.
The waters off Somalia are seen as the world's most dangerous.
Hijackings and piracy have surged in the past year as armed groups take advantage of a lack of law and order in the country, which has been without an effective central government since 1991.
Mr Ghedi is part of a transitional administration which only controls parts of Somalia.
"The State Department has not negotiated any such contracts or agreements," the department said in a statement reported by Reuters news agency.
"We have held diplomatic discussions with representatives from the transitional federal government concerning a number of areas of possible co-operation, including anti-piracy efforts."
State Department spokesman Sean McCormack said US forces were generally active in the Horn of Africa region, conducting counter-terrorism operations and battling pirates, AFP reports.
The US Navy has recently seized pirates in international waters but has been unable to pursue them close to shore.
Mr Ghedi had said US Navy vessels had been granted permission to patrol Somali waters.
Under the agreement, he had said the US Navy would also develop Somalia's rudimentary coastguard service.
Two weeks ago, pirates who seized a South Korean fishing vessel and its 25 crew were able to escape from US and Dutch navy vessels by entering Somali waters.
The ship and crew are still being held.
In February, 10 Somali men accused of piracy and arrested by the US were transferred to the Kenyan port of Mombasa for trial.
Luxury cruise liners and ships carrying food aid are among those targeted off Somalia in the past year.
The maritime gangs generally use speedboats to approach ships - sometimes impounding them and their crew at gunpoint and demanding ransoms before they are released.
The International Maritime Bureau has recorded 41 attacks since mid-March last year.
In November last year, Somalia's transitional government signed a two-year contract with US company Topcat Marine Security to help fight piracy.
The BBC's Hassan Barise in Somalia says that despite the $50m contract there has been no evidence of patrols or interceptions made by the American firm.