A rough agreement is expected by March, but experts doubt whether an agreement might be reached before June’s deadline. Pictured, U.S. Secretary of State John Kerry (L) and Iranian Foreign Minister Javad Zarif (R) before a meeting in Vienna on Nov. 23, 2014. Reuters

WASHINGTON (Reuters) - U.S. President Barack Obama and British Prime Minister David Cameron on Friday pushed back against calls for further sanctions on Iran now over its nuclear program, saying such action could harm ongoing negotiations.

In a joint news conference, Obama and Cameron urged U.S. lawmakers to exercise patience and hold off on any legislation calling for further sanctions.

"There is no good argument for us to try to undercut, undermine the negotiations until they've played themselves out," Obama told reporters. "Congress needs to show patience," he added.