Kazakhstan carrier Air Astana is raising frequency from Heathrow.
The airline is adding a fifth weekly flight to Astana from June 4.
The Sunday service complements existing departures on Mondays, Tuesdays, Thursdays and Saturdays.
The new frequency has been timed ahead of Astana’s hosting of Expo 2017.
The airline offers same-day connections to Kazakhstan’s second city of Almaty and international destinations including the Kyrgyzstan capital of Bishkek, Urumqi in north-west China, Tbilisi in Georgia and the Russian cities of Novosibirsk and Yekaterinburg.
Air Astana operates a Boeing 757 on the London route in a three class configuration comprising 16 seats in business, up to 12 economy sleeper seats and 108 in economy.
Return fares start at £498 in economy, £1,505 for economy sleeper, and £1,968 in business class.