Iranian gunboats intercepted an Iraqi speedboat filled with explosives in Iranian waters, U.S. Navy officials confirmed to Fox News Thursday, adding that they continue to be extremely vigilant for further Iraqi coastal activity.

Navy officials confirm the incident and say several similar boats also feared to be carrying explosives escaped back up the Shaat al Arab waterway, which marks the border between the two countries.

The Navy has been worried about this "fast boat" threat, which could threaten coalition vessels or commercial shipping. Keeping the waterway open for humanitarian aid and to move ships through and give them safe harbor are crucial on the agenda of naval coalition forces.

SEAL Special Boat units, Coast Guard and air assets are keeping a very close eye on any activity on the waterways, and have discovered several vessels laden with mines, Fox News learned.

U.S. Central Command discovered a sophisticated influence mine set in the channel to Umm Qasr and showed a picture of it at Thursday's briefing in Qatar. 

The arrival of the first relief ship, Sir Galahad, has been held up by the discovery of this mine.  The sinking of a vessel in the narrow channel would pose a real problem for reopening the port and pumping in significant amounts of relief supplies, Fox News learned.

The Sydney Morning Herald reported Wednesday night that coalition naval forces were on high alert against suicide attacks after the speedboats, packed with half a ton of high explosives, were intercepted. The explosives were discovered after one of the Iraqi boats was run aground during the confrontation.

The Herald reported that three other Iraqi speedboats, feared to be carrying the same amounts of explosive, escaped when Iranian forces engaged Iraqis at the mouth of the waterway.

All 30 Navy and Royal Fleet auxiliary vessels in the Gulf have mounted round-the-clock force protection squads on deck, The Herald reported, and all have permission to open fire on vessels if they continue to close on a ship after ignoring signals and warning shots across the bow.

Since the suicide boat attack against the USS Cole in October 2000, which killed 17 American sailors, and the ramming of the French oil tanker, the Linburg in 2002, warships in the area from Britian, America and Australia have been on high alert for Al Qaeda strikes.

However, the intervention of the Iraqi speedboat is the first tangible evidence that attacks are being plotted in the region.

Before Operation Iraqi Freedom stated Rear Admiral David Snelson, the British naval commander in the Gulf, told The Herald that the threat of small speedboats packed with explosives was "uppermost in his mind" in terms of threats to the Royal Navy.

Fox News' Major Garrett contributed to this report.