Turkish and Russian government officials are in an “advanced stage of negotiations” to buy 48 Su-35 Russian jet fighters, Defense News reported, citing a Turkish procurement official. The news was later confirmed by the pro-government Daily Sabah.

If confirmed, that will be the second biggest Russo-Turkish deal after the $2,5bn purchase of Russia’s S-400 long-range air defence system in July.

The new procurement deal could deepen the wedge between Turkey and its NATO allies. It is also a response to the US decision to end Turkey’s role in the production of the US F-35 Lightning II fighter jet. According to NATO officials, the expulsion became necessary due to the need to maintain the F-35s defence stealth fighter features.

Russian Su-35 carries a price tag of $50-to-70 million, which is less than half of the $95-to-$120 for an F35. However, the Turkish procurement policy is calling into question Ankara’s relationship with NATO.

Turkish President Recep Tayyip Erdogan will visit Washington on November 13, where President Donald Trump is expected to offer a Patriot missile deal before the S-400 system becomes operational. However, following the recognition of the 1915 Armenian genocide by the US Congress, there is speculation Erdogan could cancel the visit.

Turkey aspires to develop its first national fighter jet by 2023. According to the Turkish press, the Russian deal could entail technology-transfer elements, allowing Turkey to advance its federal jetfighter program.