U.S. President Barack Obama says international steps to impose new sanctions on Iran are moving "fairly quickly," after Tehran stepped up its enrichment of uranium.
Speaking at the White House Tuesday, Mr. Obama said Iran appears to have ignored his offer of engagement.
Iran said earlier that it had begun to boost enrichment to 20 percent in order to fuel a medical nuclear reactor. Tehran says its nuclear program is for peaceful purposes, but Western countries suspect it is being used to develop nuclear weapons.
The U.N. Security Council has already imposed three rounds of sanctions against Iran for its failure to halt uranium enrichment.
Russia's national security chief (Nikolai Patrushev) said Iran's decision to boost uranium enrichment has raised doubts about the peacefulness of its nuclear program.
Russia traditionally has been reluctant to impose sanctions against Iran, but Russian officials recently have shown a willingness to take a tougher position toward Tehran.
Israeli Prime Minister Benjamin Netanyahu called for immediate and "crippling sanctions" against Iran for its controversial nuclear drive. Iran considers Israel an arch-foe and has called repeatedly for its destruction.
The U.N. brokered a deal with a group of world powers that called for Tehran to ship its uranium abroad for enrichment and have it returned as reactor fuel. But Iran gave mixed signals about its willingness to accept the deal.
China on Tuesday again called for dialogue to resolve the dispute. Beijing has opposed additional sanctions against Iran.