Iran has sentenced an alleged US spy to death and imprisoned three others including an alleged British agent.

Three people face 10-year prison sentences, one of them accused of spying for Britain and another specifically accused of working for the CIA.

The death penalty case was said to be under appeal in the Supreme Court.

'One person has been sentenced to death for spying for America, ... but the ruling has been appealed', said judiciary spokesman Gholamhossein Esmaili.

Iran - whose leader Hassan Rouhani is pictured - has sentenced an alleged US spy to death and imprisoned three others including an alleged British agent

The other two alleged U.S. spies, identified as Ali Nafarieh and Mohammad Ali Babapour, received 10-year sentences in final decisions from an appeals court.

The alleged British spy was named as Mohammad Aminnassab.

Iran has made frequent claims of espionage against Britain and the United States and it is unclear how these cases relate to earlier allegations.

In July, Iran said it had broken up a CIA spy ring and sentenced some of its alleged members to death.

Some of the suspects were recruited by a 'visa trap' in which the CIA would target Iranian nationals as they applied to visit America, Iran claimed.

A documentary which aired on Iranian TV at the time purported to show U.S. agents trying to recruit Iranian spies in the Middle East.

U.S. Secretary of State Mike Pompeo retorted in July that Iran has a 'history of lying'.

Britain and Iran also remain at loggerheads over the detention of dual national Nazanin Zaghari-Ratcliffe on spying charges.

The mother-of-one was arrested in 2016 and has been kept in solitary confinement for some of her time in prison.

The latest announcement comes amid ongoing Middle East tensions, especially over Iran's nuclear ambitions.

Tehran has scaled back its commitments under the 2015 nuclear deal since Donald Trump abandoned the pact and re-imposed sanctions last year.

Rouhani has said he would consider meeting with Trump if sanctions were lifted, but Trump instead announced an increase in sanctions on Iran last month.

On top of that, a series of alarming incidents on Gulf ships - widely blamed on Iran, but always denied - have added to fears of a sudden conflict.