The current round of expert-level negotiations on the implementation of an interim nuclear deal reached in November between the six world powers and Iran have been progressing slowly and aren’t likely to see a breakthrough, a senior Iranian diplomat said on Saturday.

The talks, which began last Thursday in Geneva, Switzerland, were initially meant to run until Friday but were extended through Saturday.

“The talks that extended to a third day are making progress but slowly,” deputy foreign minister Abbas Araqchi told Iranian state-run television, according to AFP.

The state-run IRNA news agency quoted Araqchi as saying that his country was “not optimistic about any” of the world powers participating in the negotiations — the United States, Russia, China, France, Britain, and Germany.

“We entered the talks with pessimism,” he said.

The latest round of negotiations commenced a week after an Iranian delegation abruptly abandoned talks in protest over US enforcement of existing sanctions.

The interim deal — curbing but not freezing Iran’s nuclear program in return for an easing of non-core sanctions — was reached in Geneva last month, but has not been implemented because its “technical details” have yet to be finalized.

The Obama administration announced Thursday that it would veto a newly proposed Senate bill that would increase sanctions against Iran should the country fail to comply with the terms of the interim nuclear deal.

Iranian Foreign Minister Mohammad Javad Zarif has indicated that such legislation, if passed, would torpedo the ongoing talk.

On Saturday, Araqchi said that the administration’s announcement that it would veto the sanctions bill should it be passed did not inspire any optimism in Tehran.