U.S. special envoy for Iran Robert Malley said on Tuesday that Tehran is just “a matter of weeks” away from having enough enriched uranium for a nuclear weapon.

In an interview with National Public Radio, Malley said that last week’s indirect talks between Washington and the Islamic Republic geared towards reviving the 2015 nuclear deal were “more than a little bit of a wasted occasion.”

Malley revealed that a comprehensive proposal that the United States was prepared to accept had been presented, and that the only “party that has not said yes [to it] is Iran.”

“The European Union—in its role as coordinator—wanted to try one more effort, at least one more effort, and so they invited both delegations [from Iran and the United States] to meet them in Doha in the hope that Iranians would show something, some willingness to get to yes,” said Malley, who led the American team of negotiators.

But, he continued, it “seem[s] at this point [Tehran is] not capable of providing answers.”

The discussion that needs to take place, he said, “is not so much between us and Iran, although we’re prepared to have that, it’s between Iran and itself … They need to come to a conclusion about whether they are now prepared to come back into compliance with the [2015 nuclear deal] deal.”

Malley said Iranian representatives had made new demands in Doha, but provided no details.