WASHINGTON (CNN) - A U.S. Navy ship protecting commercial shipping from pirates seized about 4 tons of hashish being transported aboard a boat off the Horn of Africa last week, the Navy said in a statement released Tuesday.

The ship, the guided missile cruiser USS Anzio, on Thursday stopped a small boat known as a skiff in the Gulf of Aden because of suspicions it was a pirate boat, according to the Navy's 5th Fleet, based in Bahrain. A Navy boarding team discovered the drugs, it said.

The Navy estimated the value of the hashish at U.S. $28 million. The boarding team dumped it into the ocean, the Navy statement said.

The boat was stopped about 170 miles southwest of Salalah, Oman, it said.

The Anzio is part of the coalition effort to reduce pirate's attacks in the waters off Somalia.

The area is a major transit point for commercial shipping into and out of the Red Sea. Somalia-based pirates have captured or attempted to capture scores of merchant ships there. Navy officials said the area also is a very popular drug smuggling route, with money from drug sales possibly ending up in the hands of terrorists in Afghanistan.