Moscow ? The chief of Russia’s space agency said that the United States has rejected a proposal for the two countries to explore the moon together, a Russian news agency reported.

A NASA spokesman in Washington said the U.S. was unaware of any Russian proposal, and was perplexed by the space chief’s claim.

NASA announced in December that it would establish an international base camp on one of the moon’s poles, permanently staffing it by 2024. Officials with Russia’s federal space agency, Roscosmos, later said they had hoped to join NASA’s program, contributing Russian technology and space experience.

But Roscosmos chief Anatoly Perminov was quoted by the Interfax news agency Sunday as saying that the United States had rebuffed the offer.

“We are ready to cooperate but for some reasons the United States has announced that it will carry out the program itself,” he was quoted as saying on TV.

Michael Braukus, a NASA spokesman in Washington, said the agency had received no lunar exploration proposal from Roscosmos. “We haven’t rejected anyone’s proposal,” he said. “We are really into involving the international community in this.”