Associated Press reported that an Iranian official said Sunday the country has increased production to more than 300 metric tons of a gas used for uranium enrichment, a semiofficial news agency reported.

The announcement comes as the U.N. Security Council is deciding on imposing further economic sanctions against Iran for refusing to roll back its nuclear activities.

“The Isfahan uranium conversion facility is active, and it has produced more than 300 tons of UF6,” otherwise known as uranium hexaflouride gas, said Javad Vaidi, deputy of Iran’s Supreme National Security Council, in a meeting with members of the Revolutionary Guards.

The central Iranian cities of Isfahan and Natanz house the heart of the Iran’s nuclear program. In Isfahan, a conversion facility reprocesses raw uranium, known as yellowcake, into uranium hexaflouride gas. The gas is then taken to Natanz and fed into the centrifuges for enrichment.

A report by U.N nuclear watchdog in November confirmed Iran had stockpiled nearly 270 tons of the precursor gas used in enrichment.

The U.N. Security Council has been trying to pressure Iran to freeze uranium enrichment. But Iran has repeatedly refused, and officials from the International Atomic Energy Agency have privately said Tehran is expanding the program.

The Security Council is considering a new draft resolution that calls for additional sanctions against Iran, including bans on travel. Two sets of sanctions have already been imposed on Iran for refusing to halt enrichment.