The Turkish lira weakened on Thursday after US President Donald Trump pushed President Tayyip Erdogan to walk away from the purchase of a Russian missile defence system, calling it a "very serious challenge" to bilateral ties.

The lira stood at 5.7620 against the dollar at 0635 GMT, weakening some 0.3% from Wednesday's close of 5.7450. The Turkish currency has weakened around 8% this year, mainly on concerns over deteriorating US ties.

Shares in Halkbank fell 3% at the opening and were down 1.85% at 0715 GMT. The main share index was up 0.28%.

The lira came under pressure earlier this year as Ankara faced US sanctions due to its purchase of the Russian S-400s. It also weakened in October when Turkey launched an operation in northeast Syria against the Kurdish YPG militia, a US partner, again raising the prospect of sanctions.