In March, President Donald Trump said the two leaders would meet soon. But since then already-fragile ties between Washington and Moscow have been strained further by the conflict in Syria and the poisoning of a former Russian spy in Britain.

Russian President Vladimir Putin said last month the proposed summit was beset by problems and would not go forward now.

Putin was asked by Austrian broadcaster ORF why it was taking so long to arrange, he said, “You have to ask our colleagues in the U.S.A. In my view it is the consequence of the fierce domestic political contest in the United States.” Putin also said that Trump and he talk “regularly” over phone.

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Trump is under pressure from special counsel Robert Mueller’s investigation into whether Russia meddled in the 2016 U.S. election and whether there was collusion with Trump’s campaign – something both he and Moscow deny.

“In one of our last discussions, Donald said he is concerned about the danger of a new arms race. I agree with him entirely,” Putin said.

Trump made a similarly vague reference to the issue in April, when he said, “Stop the arms race?” in a tweet that also mentioned providing “help” for the Russian economy.