DUBAI—U.S. Marines early Thursday boarded and seized control of a German-owned commercial vessel that had been commandeered by pirates, in what appeared to be the first American-led military boarding of its kind amid a recent surge of attacks in the Gulf of Aden and along the east coast of Africa.

A raiding party of 24 Marines boarded the ship about 85 miles southeast of Mukallah, Yemen, in the Gulf of Aden, according to the U.S. Navy. Pirates had captured the vessel, which was carrying steel chains, in the same vicinity the previous day, the Navy said.

The U.S. said there were no casualties among the raiding party or the ship's crew. Nine alleged pirates were captured in the operation.

The Gulf of Aden, a waterway connecting the Red Sea with the Arabian Sea and Indian Ocean, is an important shipping route for goods going to and from Europe and Asia. It is also an important oil supply line, with Saudi Arabia shipping some of its exports through the passage.

Somalia-based pirates started to ratchet up their attacks in the gulf and along the east coast of Africa in 2008. In January 2009, the U.S. set up Combined Task Force 151, designed specifically to fight the new piracy threat. Other bodies, including the European Union, have established their own maritime task forces, which tend to operate in coordination with one another, and with individual navies. Iranian and Chinese ships have also cooperated in more informal ways in the fight against piracy in the region.