British Prime Minister David Cameron will hold face-to-face talks with Iranian President Hassan Rouhani, the premier's office said on Tuesday, in what would be the first such high-level meeting between the two countries since 1979.
During the meeting at the sidelines of the United Nations summit in New York, Cameron will urge Rouhani to join an international campaign against Islamic State (IS) jihadists.
The planned talks come after rare direct talks between US Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif.
The approaches to Tehran reflect determination by Western leaders' to enlist the support of powers in the region to tackle the jihadist group.
The IS organisation, which has seized swathes of territory in Iraq and Syria, has carried out scores of atrocities including beheadings and crucifixions.
Cameron vowed to destroy the group after its militants killed British aid worker David Haines and threatened further British hostages earlier this month, but has stopped short of joining US and French airstrikes and has ruled out sending troops to Iraq.
The British leader is expected to call on the world to come together to defeat extremist groups such as IS in a speech at the UN General Assembly.
British ties with Tehran, which broke down after Iran's Islamic revolution in 1979, have slowly warmed since a low point three years ago when protesters stormed the British embassy.
Tehran, long isolated due to tensions over its nuclear program, rejects Western accusations that it hopes to develop nuclear weapons, insisting its programme is peaceful.