British Prime Minister Keir Starmer arrived in Turkey on Monday aiming to advance negotiations on a multi-billion-dollar sale of Eurofighter Typhoon jets to enhance Ankara`s air capabilities.

Starmer is scheduled to meet with President Recep Tayyip Erdogan on regional and bilateral issues.

In July, Turkey and the UK signed a preliminary deal for the Eurofighters, which are manufactured by a consortium comprising the UK, Germany, Italy and Spain and led by Britain`s BAE Systems. The deal followed Germany`s reported decision to lift its longstanding opposition to the sale of the jets to Turkey.

Last week, Erdogan toured three Gulf nations and held talks on the potential acquisition of used Typhoons from Qatar and Oman.

Starmer`s spokesperson, Tom Wells, said the prime minister is "optimistic that he will soon conclude negotiations with our Turkish partners on a multibillion-pound deal to equip them with Typhoon fighter jets."

The British leader`s visit comes as Turkish prosecutors on Monday filed new charges against Istanbul`s jailed mayor, Ekrem Imamoglu, accusing the politician seen as a key challenger to Erdogan of involvement in "espionage" activities. Imamoglu was arrested in March on corruption charges, which he strongly denies.

Turkey`s main opposition party, the Republican People`s Party, or CHP, has criticized European governments for their muted responses to what they see as a politically motivated government crackdown on Imamoglu and other jailed opposition mayors. Erdogan`s government insists the courts operate independently.

Wells said the U.K. expects Turkey "to uphold its international obligations and the rule of law, including the right to a fair trial," adding that London had raised the issue of the arrests with Turkey`s government "at a number of levels."

"We have always been very honest with our counterparts over areas of divergence," Wells said when asked about Turkey`s human rights record. "Economic partnership can coexist with frank dialogue on areas of disagreement."

Turkey views the purchase of Eurofighters and other advanced jets as an interim solution until its domestically developed fifth-generation KAAN fighter jet becomes operational. That is expected no earlier than 2028.

Turkey, a member of the NATO military alliance, also seeks reentry into the U.S.-led F-35 fighter jet program. It was excluded in 2019 due to its purchase of Russian-made S-400 missile defense systems, which was deemed a security risk to the F-35 program.

Erdogan raised the issue of the sale of F-35 fighter jets during a recent meeting with U.S. President Donald Trump at the White House.

Turkish officials have said Turkey wants to acquire a total of 120 fighter jets - 40 Eurofighters, 40 U.S.-made F-16s and 40 F-35s - as a transitional fleet ahead of the KAAN`s entry into service.

On Monday, Starmer visited the Turkish Aerospace Industries` facility in Ankara, where he received a briefing on the KAAN fighter jet, Turkey`s defense ministry said.

Associated Press writer Jill Lawless contributed from London.

This version corrects to say that the new charges against the mayor were filed on Monday.