New Delhi, Feb 17 : NATO Secretary-General Jens Stoltenberg has said the alliance is concerned that Russia is "trying to stage a pretext for an armed attack against Ukraine", The Guardian reported. He was asked by the Wall Street Journal about Kremlin's comments blaming Kyiv for the shelling in Donbas. Stoltenberg said, "We are concerned that Russia is trying to stage a pretext for an armed attack against Ukraine. There is still no clarity, no certainty about Russia's intentions." "Russia has amassed the biggest force we have seen for decades," he added. Meanwhile, US Defense Secretary, Lloyd Austin, has alleged that Russia is moving troops closer to Ukraine borders and stocking up on blood supplies in anticipation of casualties on the battlefield, The Guardian reported. "I was a soldier myself not that long ago. I know first-hand that you don't do these sorts of things for no reason," said Austin, a retired army general. "And you certainly don't do them if you're getting ready to pack up and go home. We see them fly in more combat and support aircraft. We see them sharpen their readiness in the Black Sea," Austin said at NATO headquarters in Brussels, adding: "We even see them stocking up their blood supplies." On its part, Moscow has denied that it is planning to invade Ukraine, claiming that it is pulling back some troops. /IANS