The lira closed at 5.9955 against the US dollar on Friday, after hitting its weakest level in more than seven months at 6.2460 on Thursday.

Four sources confirmed the banks' efforts on Friday to protect the lira.

"The state banks intervened again between 1800-2000 GMT," an investor source said.

"So [there were] two interventions in the relatively thin end-of-day US timezone," the source added, referring to Friday and to dollar selling the previous day.

"We clearly started to notice Turkish banks are in the market after the lira firmed to 6.10 against dollar on Friday," a senior forex trader at a bank said.

"Banks offered US dollars until the market was completely illiquid."

The lira has lost as much as 15 percent against the dollar this year, with the latest weakness driven by investor concerns over Monday's decision to re-run a mayoral election in Istanbul that had been narrowly won by the main opposition party.

Turkey's central bank on Thursday effectively tightened policy by funding the market through a higher rate and took additional liquidity steps to bolster the lira.

A rally on Friday in Turkish bonds was driven by buying by local pension funds, the investor source said adding there was "zero sign of offshore buyers" for bonds.

A bond rally boosts the country's currency.