(Reuters) - Powerful Russian anti-ship missiles acquired by Hezbollah give it the means to deliver on its leader's veiled threat against U.S. warships and underline the grave risks of any regional war, sources familiar with the group's arsenal say.

Hezbollah leader Sayyed Hassan Nasrallah warned Washington last week his group had something in store for the U.S. vessels deployed to the region since war erupted last month between the Palestinian group Hamas and Israel, shaking the wider Middle East.

Two sources in Lebanon familiar with the Iran-backed group's arsenal say he was referring to Hezbollah's greatly enhanced anti-ship missile capabilities, including the Russian-made Yakhont missile with a range of 300 km (186 miles).

Reports by media and analysts have for years indicated that Hezbollah acquired Yakhont missiles in Syria after deploying there more than a decade ago to help President Bashar al-Assad fight a civil war.

Hezbollah has never confirmed possessing the weapon.

The Shi'ite group's media office did not immediately respond when reached for comment for this story.

Washington says its Mediterranean naval deployment - comprising two aircraft carriers and their supporting ships - aims to prevent the conflict from spreading by deterring Iran, which backs groups including Hamas, Hezbollah, and Palestinian Islamic Jihad.

Hezbollah perceives the U.S. warships as a direct threat because of their ability to hit the group and its allies.

Nasrallah said in a speech on Friday that the U.S. warships in the Mediterranean "do not scare us, and will not scare us".

"We have prepared for the fleets with which you threaten us," he said.

The White House said after Nasrallah delivered his Friday speech that Hezbollah must not exploit the Hamas-Israel war, and the United States did not want to see the conflict expand into Lebanon.

One of the sources said Hezbollah's anti-ship capabilities had developed enormously since 2006, when the group first demonstrated it could strike a vessel at sea by hitting an Israeli warship in the Mediterranean during a war with Israel.

"There's the Yakhont, and of course there are other things besides it," the source said, without elaborating.

The source added that use of this weapon by Hezbollah against hostile warships would indicate the conflict had escalated into a major regional war.