US Assistant Secretary of State for Western Hemisphere Affairs Tom Shannon made the assurance in a joint media conference with Argentine President Cristina Kirchner in the capital Buenos Aires, after several Latin American nations voiced concern at the return of the US navy patrol mission for the region.

Shannon stressed that the fleet, which had been put into slumber for the nearly six decades, had no aircraft carrier or large warships in its composition.

The largest vessel in the fleet was a hospital ship, he said.
The US official admitted that Kirchner had expressed worries about the reactivation of the navy unit in talks with him, and asked pointed questions about media reports suggesting the fleet would try to sail in rivermouths.

Shannon said the fleet would enter into no river or within maritime territorial limits, which generally reach 200 kilometers (300 miles) off the coasts of countries.

The fleet, which has a changeable composition of ships, was reestablished on July 1.
It last operated in 1950. In the intervening period, it was absorbed by the US Second Fleet that patrols the Atlantic Ocean.

As well as Argentina, several leftist-run states in Latin America such as Cuba, Bolivia and Venezuela have said they fear the move signals a return to US gunboat diplomacy.

"What reason could the United States have for dispatching such a powerful naval force to a peaceful region?" Venezuelan President Hugo Chavez, a virulently anti-US leader, asked at a regional trade summit last week.

Brazil too has said it is concerned by the decision, prompting the US ambassador to that country, Clifford Sobel, to also stress Thursday the fleet would not have an offensive role.

"Some see it as a threat," he acknowledged, adding: "This is not true."
The Fourth Fleet will be mainly used for humanitarian assistance missions and to provide support for anti-narcotics operations, while respecting the sovereign maritime territorial limits of countries in the region, he told a business conference in Sao Paulo.

US Admiral Jim Stavridis has said the fleet's reinstatement was a sign of cooperation between the United States and Latin America.

Argentina, under President Kirchner and her predecessor and husband Nestor Kirchner, has had prickly relations with the United States. Washington fears Argentina may be aligning itself with Chavez.

US allegations in December that Chavez had illegally sent 800,000 dollars to Argentina with a US-Venezuelan businessman to finance Cristina Kirchner's election plunged ties to a new low.

Shannon arrived in Buenos Aires on Thursday, accompanied by senior officials from the US departments of state, justice and defense, and the US treasury undersecretary for Western hemisphere affairs, Brian O'Neill.

Their talks with Argentine government officials were also to cover economic issues, including market access, operations of regional trade blocs, biotechnology, as well as fighting terrorism and the struggle against drug smuggling, said the US ambassador to Argentina, Hector Timerman.

Shannon and O'Neil were to speak with Argentine Economy Minister Carlos Fernandez, central bank chief Martin Redrado, Buenos Aires governor Daniel Scioli, Justice Minister Anibal Fernandez and Finance Secretary Hernan Lorenzino during the trip.