DUBAI, United Arab Emirates — A new international naval force under American command will soon begin patrols to confront escalating attacks by Somali pirates after more than 100 ships came under siege in the past year, the U.S. Navy said today.

But the mission — expected to begin operations next week — appears more of an attempt to sharpen the military focus against piracy rather than a signal of expanded offensives across one of the world's most crucial shipping lanes.

The force will carry no wider authority to strike at pirate vessels at sea or specific mandates to move against havens on shore — which some maritime experts believe is necessary to weaken the pirate gangs that have taken control of dozens of cargo vessels and an oil tanker.

Pentagon officials described it as a first step to create a dedicated international structure — combining military force, intelligence sharing and coordinated patrols — to battle piracy from lawless Somalia.

The sharp spike in pirate attacks caused a "situation where there were competing priorities" between counterterrorism missions in the region and protecting merchant ships, said Air Force Lt. Col. Patrick Ryder, a Pentagon spokesman in Washington.

There currently are more than a dozen warships in the vast expanse off the coast of Somalia, from naval giants such as the U.S., Britain and Russia, emerging powers such as China and India and regional forces such as Iran.

The announcement on the new mission — issued by the U.S. 5th Fleet in Bahrain — said more than 20 nations are expected to take part.