ROME, Jan 12 (AFP) - Italian authorities have opened inquiries into two alleged near misses between Italian passenger jets and US warplanes over Sicily in December, investigators said on Friday.

The probes are likely to further strain ties between the United States and Italy, which has taken the lead in criticizing the use by American forces during the Balkans conflict of depleted uranium munitions blamed for causing a spate of cancer cases among Italian and other NATO troops.

Italy's air safety authority ANSV opened a first inquiry on December 28 after pilots from the Italian carrier Alitalia reported six near misses on flights either into or out of Sicily's Palermo airport.

Two pilots said they were forced to take evasive action to avoid aircraft in their flight paths.

A parliamentary question raised on Wednesday by communist deputies demanded to know if US, NATO or Italian air force exercises had been carried out in the area.

"There has been intense military activity in the skies which has not been reported either to pilots or to the appropriate authorities", Ugo Boghetta, of the communist PRC group said.

Air safety investigators said civilian pilots reported encountering air traffic -- most probably of a military nature -- on flight paths reserved for civilian carriers over the Tyrrhennian sea north of Sicily.

The US embassy in Rome confirmed late Thursday that warplanes from the US aircraft carrier Harry S. Truman had made sorties over the sea on December 14 and 15, but insisted that at no time did they pose a threat to other planes.

US authorities have said they are willing to cooperate fully with Italian investigators over the matter.

The same flight path was the scene of a still unexplained tragedy in 1980 in which 81 people were killed when the DC9 they were travelling in fell off the radar screen and into the sea just north of Sicily.

Italian investigators still believe the most likely explanation for the crash to be that it was shot down either by French or US fighters who mistook it for a Libyan warplane.

Both Paris and Washington continue to deny having had warplanes in the area at the time.

A further incident clouding the issue of the US military presence in Italy was an accident nearly three years ago when a low-flying US military jet sliced through the cable of the ski lift in northern Italy.

Eight Germans and twelve other Europeans were killed in the accident, which many believe was caused by reckless flying by a US navy pilot.

The disaster caused an uproar in Italy, strained relations with Washington and prompted a review of the rules for low-level training flights for US military aircraft in Italy.

The near-miss investigation has compounded tensions in US-Italian relations caused by widespread concern here over a spate of cancer cases among soldiers feared linked to the use of depleted uranium tipped shells by US forces in Bosnia and Kosovo.

On Wednesday, Italian Defense Minister Sergio Mattarella told parliament that seven Italian soldiers had died and another 23 been diagnosed with symptoms possibly linked to radioactivity from the US weapons.

He said 21 of the soldiers had served in the Balkans.

Washington insists there is no correlation between the ammunition and any cases of cancer and has rejected demands from Italy and several other NATO allies for a moratorium on the use of depleted uranium projectiles.