A U.S. State Department spokesman Tom Casey said that Under Secretary of State for Political Affairs Nicholas Burns will travel to London to consult with his Russian, Chinese, British, French, and German counterparts on the Iranian nuclear issue.
Washington has vowed to seek a new resolution to put more pressure on Iran to suspend uranium enrichment.
Enriched uranium can be used as fuel for civilian nuclear reactors, but it is also useful in the production of nuclear weapons.
Powers Of Persuasion
The five permanent UN Security Council members plus Germany have spearheaded the international response to Tehran's nuclear activities.
The International Atomic Energy Agency (IAEA) reported on February 22 that Iran has recently expanded its nuclear program by setting up hundreds of centrifuges for uranium enrichment.
The report exposes Iran to possible broader UN sanctions on top of those imposed two months ago.
In December, the Security Council adopted a resolution imposing limited sanctions specifically targeting Iran's nuclear and ballistic-missiles programs.
The United States, France, and Britain have said that they will now seek a new resolution that could lead to tougher measures. Diplomats have suggested the measures could include a travel ban and financial and other sanctions.
But Russia, a permanent member of the Security Council with economic interests in Iran, has questioned the usefulness of further sanctions.
Russia's ambassador to the UN, Vitaly Churkin, has stressed that the goal is a diplomatic solution to curb Iran's nuclear ambitions.
'We Are Cooperating Fully'
Iranian officials have dismissed sanctions and called for diplomacy while consistently refusing to suspend uranium enrichment. Iran's ambassador to the IAEA, Ali Asghar Soltanieh, insisted to Reuters after the release of the agency's report that his country wants to negotiate.
"We are fully cooperating with IAEA," Soltanieh said. "And we are suggesting to the whole world to put pressure on those who are not coming to the negotiating table to come to the negotiating table; and let's solve the problem by dialogue and negotiation rather than the sanctions and resolutions or confrontation."
Iran's president, Mahmud Ahmadinejad, today repeated his assertion that Tehran will not show weakness over what he and other officials call Iran's "nuclear rights."
Tehran says its nuclear program is entirely peaceful. But Western critics suspect that Iran is covertly seeking to produce nuclear weapons.
THE COMPLETE PICTURE: RFE/RL's complete coverage of controversy surrounding Iran's nuclear program.
An annotated timeline
of Iran's nuclear program.