The Rosaviatsiya state aviation agency has informed the transport minister that the Sheremetyevo airport project would not be ready by the June 14 kickoff, the Vedomosti business daily said.

The airport's third landing and takeoff strip was meant to nearly double the number of flights the bustling hub could handle from 55 to 90 per hour.

Vedomosti said there was also a possibility that a new runway for Moscow's number two airport Domodedovo would miss its tournament deadline.

Russia's World Cup organising committee told AFP the reported construction delays were "possible".

"The possible change of delivery of the new runways at Domodedovo and Sheremetyevo airports will not in any way affect successful execution of the 2018 FIFA World Cup Transport Plan," it said in an emailed statement.

Rosaviatsiya spokesman Sergei Izvolsky refused to confirm or deny the reported delays when contacted by AFP.

Sheremetyevo is Russia's largest airport by passenger volume, servicing 41 million people last year.

It is the main hub of the flag carrier Aeroflot, which soccer fans will also heavily rely on to reach the other 10 host cities.

An additional 31 million passengers travelled last year through Domodedovo, the airport said.

It focuses on European destinations and is used by airline majors such as British Airways and Lufthansa.

Sheremetyevo spokeswoman Anna Zakharava said the airport took into account the possibility of the runway not being completed when it prepared for the World Cup.

"In either case, we will be able to handle all the scheduled flights without a problem," Zakharova told AFP.

Vedomosti said the third runway at Sheremetyevo, which is projected to cost 64.1 billion rubles (US$1.1 billion), was only half ready in March.

All construction at the two airports must end by mid-May so as not interfere with the arrival of the first supporters and teams.

Vedomosti said Sheremetyevo's delays were caused mostly by bureaucratic red tape: the time it took to get approval for relocating existing gas and petrol pipelines, and purchasing property from local residents.

Sheremetyevo chairman Alexander Ponomarenko told Vedomosti it was "critically" important to get the third runway built this year so that repairs could begin on one of the other two.

The Domodedovo runway is meant to replace one of the existing two and will cost $225 million to build, Vedomosti said.

It was 80 percent ready but its contractor ran out of financing after being declared bankrupt in 2016, it added.

Domodedovo said in a statement that it was "completing" an expansion project, but provided no other details.

Russia is using its first World Cup to upgrade infrastructure in some of its biggest cities, investing $12 billion in new stadiums, hotels, roads and airport facilities.