Turkey is ready to discuss U.S. concerns about the technical compatibility of Russian S-400 defences and U.S.-made F-35 jets, Defense Minister Hulusi Akar said Thursday, repeating Ankara's proposal for a joint working group with Washington on the issue. U.S. President-elect Joe Biden is expected to be tougher on Turkey than was Donald Trump, particularly over its foreign and defence policies, and domestic human rights record.