The Hezbollah group may have Russian-made Yakhont anti-ship missiles (or P-800 Oniks, which are marketed for export as Yakhont) at its disposal, which it could use against US warships.

Details: Reuters noted that Hezbollah leader Hassan Nasrallah warned Washington last week that his group had "something in store for the US vessels" deployed in the region after the war between the Palestinian group Hamas and Israel erupted last month.

Two Lebanese sources with knowledge of the matter said he was referring to Hezbollah's significantly enhanced anti-ship missile capabilities, including Russian-made Yakhont missiles with an effective range of 300 kilometres.

Media reports and analysts have indicated for years that Hezbollah acquired Yakhont missiles from Syria.

Hezbollah has never before confirmed that it possessed these weapons.

One source said that Hezbollah's anti-ship capabilities have increased significantly since 2006, when the group first demonstrated that it could hit a vessel at sea by hitting an Israeli warship in the Mediterranean.

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

The source added that Hezbollah's use of these weapons against warships would mean that the conflict has escalated into a major regional war.

Three current and one former US official said Hezbollah has developed an impressive array of weapons, including anti-ship missiles.

For reference: Hezbollah is a Lebanese Shiite paramilitary Islamist organisation and political party. It is recognised as a terrorist organisation by the governments of Israel, the United States, Canada and Bahrain. The EU, the UK, Australia and the Netherlands recognise Hezbollah's External Security Organisation as a terrorist organisation.

It almost completely controls the southern part of Lebanon.