Ömer Çelik, strategist and adviser to Turkish president Erdoğan, says YPG is taking areas for its own that were taken from Isis with help of US airstrikes

A senior official in Turkey’s ruling party and close confidante of President Recep Tayyip Erdoğan said US-backed Kurdish militia in northern Syria appeared intent on creating a de facto zone of control in the region.

Ömer Çelik, a key strategist and policy maker in Erdoğan’s Justice and Development Party (AKP) said the Syrian Kurdish YPG militia and its political wing, the PYD, was forcibly removing Arab and Turkmen civilians from areas liberated from Islamic State control.

Çelik also said Turkey could not accept a transitional government in Syria led by President Bashar al-Assad and said plans for a safe zone in northern Syria for civilians had been shelved due to the lack of western political will.

“He has the blood of hundreds of thousands of people on his hands; he has more blood on his hands than Slobodan Milošević,” Çelik told the Guardian in an interview. “Even if there were a legitimate transition government, it would be impossible to imagine Bashar al-Assad as part of it. The military presence of multiple countries in Syria will make the country more like Afghanistan, not restore stability.”

Çelik’s comments indicate the thinking within the senior leadership of Turkey’s ruling party, suggesting a growing rift between Turkey and its allies on how to deal with the crisis in Syria, which is now in its fifth year with over a quarter of a million dead and two million refugees in Turkey alone.

It also complicates the American strategy in Syria, which has strongly relied on the Kurdish YPG and its Arab allies, who have retaken large swathes of territory from Isis in the north after bitter fighting with a dependence on US-led coalition airstrikes. Over the weekend, the Pentagon said it had airdropped ammunition to Syrian forces fighting Isis in the north, prompting protests by Turkey, which considers the YPG an affiliate of the outlawed Kurdistan Workers Party (PKK).

“Our position on Syria is clear: when the regime started targeting innocent civilians, there were several hundred small jihadi groups,” Çelik said. “Right now, there are tens of thousands of such groups. Unless Assad is removed from power, we’ll see additional increase in their numbers. Our western colleagues claim that radicals will replace Assad if the regime collapses. This is a misguided assumption.”

He criticised western inaction over Syria, saying it emboldened the Assad regime to harm civilians and use chemical weapons. The Turkish government recently proposed a safe zone for civilians stretching across northern Syria, but Çelik said the plans had been shelved due to a lack of political will and commitment by Turkey’s allies.

“The international community and our allies don’t have a strong track record on Syria,” he said. “Our allies should have stood in solidarity with the Syrian people and the international community should have drawn necessary lessons from their belated response to the Bosnian conflict.”

On the Syrian Kurds, Çelik said Turkey’s concerns were rooted in what they see as the PYD’s collaboration with the outlawed PKK, and the creation of a zone of control on the border with Turkey that would exclude the Arab Syrian opposition. He said Turkey backs the moderate opposition represented by the exiled Syrian National Coalition and the Free Syrian Army.

“They need to stop posing a threat to Turkey and cooperating with the PKK, and they need to stop exploiting the situation in northern Syria,” he said. “Then we would have no problem.”

Tensions and violence have increased in recent weeks between Turkey and the PKK. Following a suicide bombing in the city of Suruç in July blamed on Isis, Turkey joined the US-led coalition against the group, but simultaneously launched a major campaign against the PKK following small-scale attacks on security forces.

The government has refused to rule out PKK involvement in a double suicide bombing over the weekend in Ankara that killed scores of civilians at an opposition peace rally in Turkey’s deadliest ever terrorist attack.

Critics of Erdoğan’s government have accused it of using recent attacks as a pretext to also crack down on the Kurds, ending a ceasefire that had held since 2013.

They say the ruling AKP was attempting to strike at the popularity of rival pro-Kurdish opposition groups in an effort to secure an absolute majority in snap elections in November, which were scheduled after negotiations between the AKP and their largest rivals, the CHP, to form a coalition failed.

Çelik, who led the AKP’s negotiation team, said the opposition’s stance on Syria was a key element in the failure of the negotiations, along with disputes on education reform and Kurdish reconciliation.

“We asked them a simple question: do you feel comfortable shaking hands with Bashar al-Assad?” he said. “And there wasn’t a clear answer to that question.”

Çelik said bombings were aimed at harming the AKP’s counter-terrorism record and its popularity, contrary to opposition claims.

He also alleged that the PKK was involved in a series of violations in the run-up to the last elections, including setting up alternative courts and collecting taxes from citizens, in addition to the attacks on security forces.

“We believe that each terrorist organisation poses an equally serious threat,” he said. “But the main difference is that we’re fighting a unilateral campaign against PKK whereas we’re part of a coalition against Isis. It’s only us fighting the PKK.”