Turkish President Recep Tayyip Erdogan said on Monday he had cancelled his planned attendance at the COP26 climate conference in Glasgow because of a dispute over the security protocol.

Erdogan had been due to travel to Scotland after holding a crunch meeting with US President Joe Biden on the sidelines of the G20 summit in Rome.

But he told reporters on board his flight back to Turkey that the Glasgow event organisers had failed to address his delegation's security concerns.

"When our demands were not met, we gave up on going to Glasgow," the Anadolu state news agency quoted Erdogan as saying.

"This was not only about our own security, but also about the reputation of our country."

A report by the Middle East Eye website cites Turkish sources as saying that organisers had put a limit on the size of Erdogan's travelling delegation.

COP26 organisers issued no immediate comment.

Turkey's parliament this year finally ratified the Paris climate agreement and Erdogan has been stressing his concern for environmental issues ahead of a general election due within the next two years.

His failure to attend comes with tensions between Turkey and its main Western allies fraying on multiple fronts.

The Biden meeting almost fell through because Erdogan last month threatened to expel 10 Western ambassadors over their joint statement in support of a jailed civil society leader.

Erdogan dropped his threat after the embassies issued public statements reaffirming their commitment not to meddle in Turkey's domestic affairs.

A senior US administration official said Biden "made clear his desire (to Erdogan) to have constructive relations with Turkey and to find an effective way to manage our disagreements".

Relations have been further complicated by Turkey's purchase of a Russian air defence system and US backing for a Kurdish militia in Syria that Ankara views as a terror threat.

The Russian purchase has complicated military cooperation between the two key members of the NATO defence alliance.

Biden told Erdogan in Rome that his request for a large new shipment of F-16 fighter jets could meet resistance in Congress because of concerns about Turkish human rights.

But Erdogan told reporters on Monday that he felt reassured after discussing the F-16s order with Biden.

"We talked about the F-16 deliveries. I did not feel like they had a negative attitude about it," Erdogan was quoted as saying.