NATO members tighten security as G7 leaders discuss Russia's assault on Ukraine

U.S.-led NATO said on Tuesday its member states were boosting security around key installations as Russia escalated its attacks on Ukraine and stepped up threats against the West.

Russian missiles pounded Ukraine for a second day, after dozens of air raids across the country on Monday that killed 19 people, wounded more than 100 and knocked out power supplies.

Moscow has annexed new tracts of Ukraine, mobilised hundreds of thousands of Russians to fight and repeatedly threatened to use nuclear arms in recent weeks, spreading alarm in the West. A European diplomat said NATO was considering convening a virtual summit of the Western defence alliance to consider its response.

NATO was closely monitoring Russia's nuclear forces, but had not seen any change in its nuclear posture, Secretary General Jens Stoltenberg told reporters in Brussels.

The allies were increasing security around critical infrastructure after attacks on gas pipelines running under the Baltic Sea and any deliberate attack would be met with a "united and determined response", he said. It is still unclear who was behind the recent explosions.