The United States is reportedly blocking a $400 million plan by South Korea to sell KAI T-50 Golden Eagle trainer jets to Uzbekistan.

The aircraft, co-developed in 2006 with Lockheed Martin, uses Lockheed Martin technologies -- including avionics -- and as such requires permission under the U.S. Arms Export Control Act for its sale to other countries.

The Korea Times , quoting unidentified sources, says that permission has been refused.

"KAI has been in negotiations with the Uzbek government to export the supersonic trainers, but the U.S. government is opposing the deal, citing possible technology leakage and diplomatic policy," a source said.

Uzbekistan, located in Central Asia, was previously part of the Soviet Union. It is a member of the Shanghai Cooperation Organization, whose other members are China, Kazakhstan, Kyrgyzstan, Russia and Tajikistan.

"As Uzbekistan has close ties with Russia, the U.S. is worried that an export of T-50s to Uzbekistan may lead to its technologies being transferred to Russia," a military official was quoted by the newspaper.

"Despite the U.S. opposition, DAPA (the Defense Acquisition Program Administration) will step up efforts to persuade Washington to approve the deal."