Russia rejected a draft resolution Friday that would condemn Iran for failing to block supplies of missiles to Yemen's Huthi rebels and call for measures against Tehran, diplomats said.
The Security Council is expected to vote on Monday on the British-drafted measure that would renew sanctions on Yemen for a year and address the findings of a UN report that pointed a finger at Iran.
The report by a UN panel of experts found that Iran had violated the 2015 arms embargo on Yemen after determining that missiles fired by the Huthis at Saudi Arabia last year were made in Iran.
Britain circulated the draft resolution last week and submitted an amended text following negotiations, but Russia on Friday rejected the latest version, diplomats said.
Russia said the report's findings were too weak to justify a condemnation of Iran, diplomats said.
Negotiations were set to continue over the weekend, diplomats said.
The draft resolution "condemns" Iran for being in "non-compliance" with the arms embargo on Yemen by "failing to take the necessary measures to prevent the direct or indirect supply, sale or transfer" of short-range ballistic missiles, drones and other military equipment to the Huthis.
Backed by the United States and France, the text specifies that the council will take "additional measures to address these violations" and that "any activity related to the use of ballistic missiles in Yemen" is a criteria for sanctions.
Russian Ambassador Vassily Nebenzia on Wednesday said the draft resolution should focus on renewing the mandate of sanctions monitors for Yemen instead of taking aim at Iran.
"We don't like condemnations at all, no, in general," Nebenzia said.
"It's a resolution about the extension of the working group, not about Iran. So we should concentrate on extending the working group first," he said.
The report by the UN experts bolstered US and Saudi claims that Iran was arming the Huthis, despite Tehran's strong denials.
While the report found that Tehran had violated the embargo by failing to block the shipments, the experts said they were unable to identify the supplier.