MOSCOW — NATO released satellite photographs on Thursday showing Russian military equipment, including fighter jets and tanks, that it described as part of a deployment of as many as 40,000 troops near the border with Ukraine. The release came the same day that President Vladimir V. Putin reiterated a threat to curtail gas sales to Ukraine.

The photographs, taken by a commercial satellite imaging company called DigitalGlobe, offered some of the first documentary evidence of a military buildup that the West says Russia could use to invade Ukraine at any moment. They were released at a news conference in Belgium by Brig. Gary Deakin, the director of NATO’s Comprehensive Crisis and Operations Management Center.

The Kremlin has accused the West of exaggerating Russia’s military presence along the Ukrainian border and has insisted that it has no plans for a second military incursion after its lightning-quick occupation and annexation of Crimea. Still, Russia has warned that it may take military action to protect ethnic Russians in Ukraine if they are threatened.