JERUSALEM, April 22 (Reuters) - Israeli naval forces intercepted a cargo ship in the Mediterranean on Sunday and troops have boarded the vessel for a security check, military sources said.

Israel routinely patrols the seas for ships suspected of carrying weapons destined for Palestinian militants. A year ago Israel seized a cargo ship it said held Iranian-supplied arms intended for the Hamas-ruled Gaza Strip.

The official said so far nothing outstanding has been found on the ship, and declined to provide details, describing the interception as routine protection of our territorial waters.

An Israeli military source said the ship was seized about 160 miles (260 km) off the Israeli coast, and that troops were conducting a very thorough search of its cargo.

In the earlier searborne interception in March 2011, Israel said the vessel it seized had set sail from Syria, had stopped in Turkey and had been destined for Alexandria in Egypt.

Palestinians use a network of tunnels to smuggle weapons into Gaza from Egypt. Palestinian militants in Gaza often fire rockets at Israel and say it is in response to Israeli raids in their coastal territory.

(Writing by Allyn Fisher-Ilan; Editing by Michael Roddy)