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The US and France have vowed to work together to push for new UN sanctions over Iran's nuclear programme.
After talks in Washington with French leader Nicolas Sarkozy, US President Barack Obama said he hoped to have the sanctions in place "within weeks".
Mr Sarkozy promised "all necessary efforts to make sure Europe as a whole engaged in the sanctions regime".
Western powers suspect Iran is seeking to develop a nuclear arms capability. Tehran denies this.
It says its atomic programme is entirely peaceful.
'Mad race'
In a joint news conference with Mr Sarkozy at the White House, Mr Obama said he was not interested in waiting months for new sanctions.
"My hope is that we are going to get this done this spring," he said. "I am interested in seeing that regime in place within weeks."
For his part, President Sarkozy said Iran could not continue its "mad race" to try to complete its suspect nuclear programme.
"The time has come to take decisions. Iran cannot continue its mad race," Mr Sarkozy said at the joint press conference.
He said that he would work with German Chancellor Angela Merkel and British Prime Minister Gordon Brown to get European backing for the sanctions regime.
Mrs Merkel has suggested that if the UN Security Council cannot agree on the matter, Germany and other like-minded countries might pursue their own sanctions.
Chinese reluctance
There have been three rounds of UN sanctions against Iran, blocking trade of "sensitive nuclear material", freezing the financial assets of those involved in Iran's nuclear activities, banning all of Iran's arms exports, and encouraging scrutiny of the dealings of Iranian banks.
The US and its allies on the UN Security Council have been pushing for a fourth round of sanctions, which would target Iran's oil trade.
While Russia is thought to be more inclined than before to endorse the new sanctions, efforts to persuade China to go along have yet to bear fruit, the BBC's Paul Adams reports from Washington.
China insists fresh sanctions would "complicate the situation" and could derail diplomatic efforts.
The United States and France have announced their intention to work together in an effort to implement additional United Nations sanctions on Iran.

The announcement came after a meeting between US President Barack Obama and French President Nicolas Sarkozy. According to Obama, the two nations planned on having the new sanctions implemented "within weeks." Sarkozy pledged that the whole of Europe would be part of the plan, saying that he would make "all necessary efforts to make sure Europe as a whole engaged in the sanctions regime." He said that he planned to specifically work with German Chancellor Angela Merkel and British Prime Minister Gordon Brown in his efforts. Merkel has previously said that if the UN will not agree to implement sanctions, Germany, in concert with other nations, may introduce sanctions of their own.

Obama said that the US would not wait for an extended period of to implement new sanctions, saying that he was "interested in seeing that regime in place within weeks." Despite his commitment to the new sanctions, Obama also acknowledged the divisiveness that they provoked in other countries, saying that it was "something that we have to work on." Most notable among the opposition is China, which says that sanctions could "complicate the situation."  

There have already been three rounds of sanction enacted, which have banned trade of nuclear material, frozen financial assets of individuals and corporations engaged in nuclear activities, blocked all arms exports from Iran, and advocated for examination of Iranian banks. The proposed fourth round would target the oil trade in Iran.