The US has accused Russia of using its energy supplies “as a tool of coercion” to try to control Ukraine.
It comes after Russia warned European countries of possible gas supply cuts because of Ukraine’s energy debts.
Separately, Nato has defended the accuracy of satellite images which it says show Russian troops massed on the Ukrainian border in recent weeks.
A Russian official earlier said the images depicted a military exercise that was held in August last year.
Nato says the satellite images it unveiled early on Thursday show some 40,000 Russian troops near the border in late March and early April. They also reveal sophisticated warplanes and helicopters.
Later, Nato released additional images, some dating back to 2013 and others from early 2014, purporting to show the same areas unoccupied prior to March.
In a statement, the alliance says the images show that Russian claims that they are old were “categorically false” and that there was no evidence of military activity in these areas in 2013 or early 2014.