SINGAPORE- Vietnam is in talks with European and U.S. contractors to buy fighter jets, maritime patrol planes and unarmed drones, sources said, as it looks to beef up its aerial defenses in the face of China's growing assertiveness in disputed waters.

The battle-hardened country has already taken possession of three Russian-built Kilo-attack submarines and has three more on order as part of a $2.6 billion deal agreed in 2009. Upgrading its air force would give Vietnam one of the most potent militaries in Southeast Asia.

The previously unreported aircraft discussions have involved Swedish defense contractor Saab (SAABb.ST), European consortium Eurofighter, the defense wing of Airbus Group (AIR.PA) and U.S. firms Lockheed Martin Corp (LMT.N) and Boeing (BA.N), said industry sources with direct knowledge of the talks.

Defense contractors had made multiple visits to Vietnam in recent months although no deals were imminent, said the sources, who declined to be identified because of the sensitivity of the matter. Some of the sources characterized the talks as ongoing.

One Western defense contractor said Hanoi wanted to modernize its air force by replacing more than 100 ageing Russian MiG-21 fighters while reducing its reliance on Moscow for weapons for its roughly 480,000-strong military.

Vietnam has ordered about a dozen more Russian Sukhoi Su-30 front-line fighters to supplement a fleet of older Su-27s and Su-30s.

"We had indications they want to reduce their dependence on Russia. Their growing friendship with America and Europe will help them to do that," said the defense contractor.

U.S. Defense Secretary Ash Carter, during a visit to Vietnam on Sunday, pledged $18 million to help Hanoi buy U.S. patrol boats. But any deal with Lockheed or Boeing would likely be the most significant involving a U.S. firm since Washington started easing a long-time embargo on the sale of lethal weapons to Vietnam in October.

Boeing said in an email it believed it had capabilities in "intelligence, surveillance and reconnaissance platforms that may meet Vietnam's modernization needs". It gave no specifics.