Turkish President Tayyip Erdogan leaves a mosque after attending the Eid al-Fitr prayers to mark the end of the holy month of Ramadan in Istanbul, Turkey, June 4, 2019. REUTERS/Murad Sezer

ISTANBUL (Reuters) - President Tayyip Erdogan said on Tuesday it was out of the question for Turkey to take a step back from its deal with Moscow to buy Russian S-400 missile defense systems.

Speaking to reporters after morning prayers, Erdogan also said an offer from the United States to sell Patriot missiles to Turkey was not as good as the Russian offer.

“There is a certain step that we took, there is an agreement here and we are committed to it,” Erdogan said of the deal with Moscow. “It is out of the question for us to take a step back.”

Turkey’s deal to buy the Russian S-400s, which could be delivered within weeks, has alarmed Washington and Turkey’s other Western NATO allies, who say the Russian system is incompatible with NATO’s defense network and poses a threat to U.S. F-35 fighter jets that Turkey also plans to buy.

Erdogan said Turkey had offered to set up groups with the United States to work together on the issue, without saying what Washington’s response had been. He also said Turkey had also been discussing a U.S. offer to sell Patriot missiles.

“However, unfortunately the U.S. side has not given us an offer as good as the S400s,” he said.