British Airways is resuming direct flights to Tehran on Thursday after an interruption of nearly four years, in another sign of Iran's warming ties to Western countries.

The flagship British carrier said there would be six flights a week to Tehran's Imam Khomeini International Airport, with plans to ramp up to a daily service later this year.

The signing of a landmark nuclear accord with world powers last year led to a lifting of economic sanctions that was expected to bring huge economic benefits for Iran.

"The recent lifting of sanctions has also effectively allowed Iran to reopen for business and paved the way for commerce to reconnect with Iran's economy," said Sean Doyle, British Airways' head of network and fleet.

Ties between Britain and Iran had been particularly frosty since a crowd attacked the British embassy in Tehran in 2011, during protests against economic sanctions. The embassy was reopened in August last year.

The date for starting the London-Tehran flights had originally been planned for July. It was postponed for "technical issues", according to the carrier.

In April, after a eight-year break, Air France resumed its flight to the Iranian capital, however not without controversy.

Some female staff objected to Iran’s rules requiring them to cover their heads whenever they are not on board planes. Eventually, the French airlines agreed to let female crew members opt out of flying to Tehran.