The Turkish president will seek to persuade Donald Trump to reverse his “mistaken and shortsighted” plan to arm Kurdish forces in Syria, announced as part of an American attempt to crush Islamic State’s final stronghold in Raqqa.

US officials this week announced a deal to directly supply arms to the People’s Protection Units (YPG), a Kurdish militia that Turkey has long argued is a terrorist organisation affiliated with its own homegrown Kurdish insurgent group, the Kurdistan Workers’ party (PKK).

In a wide-ranging speech in London on Friday, the Turkish prime minister, Binyali Yıldırım, described the Americans’ chosen partners as “not humans. They are machines that kill people. They are people that will fight for whichever government gives them money.”

Yıldırım suggested that even Trump’s White House team had wanted a different plan for Raqqa, but were rebuffed by staff in the field linked to the old Obama administration.

Turkey’s president, Recep Tayyip Erdoğan, is due in Washington next week, a visit he himself has described as “a milestone”.

The Pentagon has long regarded the YPG as the most effective fighting force in northern Syria, where Isis has held swaths of territory.

The jubilant US-backed Syrian Kurdish fighters say they expect to push on and capture Isis’s de facto capital of Raqqa this summer, after receiving a range of heavy weapons from the US military.

Kimberley Taylor from Blackburn is part of the all-female Kurdish force battling to rout Islamic State. Driving them on is the chance to free women enslaved by the extremists: ‘It starts with fighting Daesh, then the mentality of the male’

A commander, identified only as Abdelqader, declined to specify dates at a press conference on Friday, citing tactical reasons.

Local forces have been buoyed following this week’s capture of the key town of Tabqa and the nearby dam, Syria’s largest. The advance has left no significant Isis-held urban settlements between ally-held territory and Raqqa.

The Turkish deputy prime minister, Nurettin Canikli, insisted the US decision should not reflect poorly on Turkish military prowess. Speaking at an event in London, he said: “Turkey has been the only country that has boots on the ground and very successfully pushed Isis away over 2,000 sq km of area in Syria.”

Questioning the alliances the US makes during conflict, he added: “They have made these mistakes in Afghanistan and Iraq, and now they are making the same mistake in Syria.”

In talks on Thursday, the US defence secretary, James Mattis, tried to assure Yıldırım that forces for the YPG in Syria would not be allowed to filter into Turkey. He also vowed that the YPG would not seek to stay let alone govern Raqqa, a predominantly Arab Sunni

Erdoğan’s trip to Washington will also be a moment for him to lobby for the extradition of Fethullah Gülen, a cleric the Turkish government claims orchestrated the failed coup of 2016.

A complete rebuff by Trump on both fronts would be a severe blow, and might send Turkey further into the arms of Russia, with which it has been repairing its damaged relationship.