WASHINGTON, Jan 13 (AFP) - The Biden administration has told Congress it is preparing the potential $20 billion sale of F-16 fighter jets to Turkey, sources familiar with the matter said on Friday, sparking an immediate objection from a senior U.S. lawmaker who has long opposed the deal.

The State Department sent the informal notice to Congress on Thursday, three sources said, informing committees overseeing arms sales in the Senate and House of Representatives of its intention to proceed with the proposed deal.

NATO member Turkey requested in October 2021 to buy 40 Lockheed Martin Corp F-16 fighters and nearly 80 modernization kits for its existing warplanes. Technical talks between the two sides recently concluded.

The Biden administration has said it supports the sale and has been in touch for months with Congress on an informal basis to win its approval. However, it has failed so far to secure a green light.

"As I have repeatedly made clear, I strongly oppose the Biden administration’s proposed sale of new F-16 aircraft to Turkey," Senator Bob Menendez, Democratic chairman of the Senate Foreign Relations Committee, said in a statement.

While the sale is still in the informal review process, Congress is also unlikely to approve the sale as long as Turkey refuses to proceed with the ratification of Sweden and Finland's NATO membership.

The two countries ended decades of neutrality last May and applied to join NATO in response to Russia's invasion of Ukraine, but Turkey objected and accused the countries of harboring militants, including from the outlawed Kurdistan Workers' Party (PKK), and demanded steps be taken.

At a press conference on Saturday, Ibrahim Kalin - a spokesman for Turkish President Tayyip Erdogan and his chief foreign policy advisor - said Washington's demands relating to the supply of the fighter jets were "endless".

"If they keep pushing Turkey in other directions with F-16 (and) F-35 sanctions, and then Turkey reacts, they blame Turkey again, then that's not a fair game," Kalin said. "It looks like their list of demands is an endless. There's always something."