Iran will convert more of its higher-grade enriched uranium into reactor fuel under an extended nuclear deal with world powers, making the material less suitable for building atomic bombs, a diplomatic source told Reuters on Monday.

Last week, Iran and the United States, France, Germany, Britain, China, and Russia failed to meet a November 24 deadline for resolving their dispute over Tehran’s nuclear program. They gave themselves until the end of June for further negotiations.

It was the second time this year they had missed a self-imposed target for a comprehensive agreement under which Iran would curb its nuclear program in exchange for an end to sanctions hobbling Tehran’s economy.

As a result, a preliminary accord reached in late 2013 will remain in force. Under its terms, Iran halted its most sensitive nuclear activity in return for limited easing of sanctions.

Accordingly, Iran earlier this year eliminated its stockpile of uranium gas enriched to a fissile concentration of 20 percent, a relatively short technical step away from weapons-grade material. A large part of it was processed into oxide.

When the deal was first extended in July, Iran undertook to move further away from potential weapons material by converting 25 kg of the uranium oxide – a quarter of the total – into nuclear fuel during the initial four-month extension.

The diplomatic source said Iran would now continue this work and he suggested around 5 kg would be converted per month, according to Reuters.

In a letter seen by Reuters on Monday, Iran and the six powers asked the UN nuclear watchdog to continue checks that Tehran is honoring its undertakings, including “monitoring of fuel fabrication” for a Tehran research reactor.

The governing board of the UN atomic watchdog agency will hold an extraordinary meeting in Vienna on December 11 to discuss its monitoring of the nuclear deal extension.

The Islamic Republic hotly denies its nuclear program is meant to build a nuclear weapon, even though the UN’s International Atomic Energy Agency (IAEA) has revealed Iran is not abiding by the interim conditions in refusing to answer questions on the military aspects of its program.