More than 50 countries will gather on the sidelines of a NATO meeting in Brussels on Wednesday to discuss bolstering Ukraine's air defence, two days after Russian missiles rained down on cities across the country, including the capital Kyiv.
The gathering in Brussels is the first big NATO meeting since Moscow annexed several Ukrainian territories, announced a mobilisation and issued veiled nuclear threats - moves that the alliance has classified as a clear escalation of the Russia-Ukraine war that started on Feb 24.
Attacks on the Nord Stream pipelines running under the Baltic Sea have contributed to heightening the tensions, although it remains unclear who was behind the explosions.
On Wednesday, Polish operator PERN said it had detected a leak in one pipeline in the Druzhba system that carries oil from Russia to Europe, though it said the cause was probably an accident, according to Reuters.
NATO warned Moscow on Tuesday that it would meet attacks on allies' critical infrastructure with a "united and determined response".
NATO chief Jens Stoltenberg pledged to boost the protection of critical infrastructure, saying NATO had already doubled its presence in the Baltic and North Seas to more than 30 ships supported by aircraft and undersea activities.
Speaking ahead of a two-day meeting of the alliance's defence ministers, Stoltenberg said that while the alliance had not seen any changes in Russia's nuclear posture, it was vigilant and would proceed with its annual nuclear preparedness exercise next week.
He was referring to the "Steadfast Noon" exercise, in which NATO air forces practise the use of US nuclear bombs based in Europe with training flights, without live weapons.
Cancelling the drills because of the war in Ukraine would send a "very wrong signal", Stoltenberg said.
"It's an exercise to ensure that our nuclear deterrent remains safe, secure and effective," he remarked, adding NATO's military strength was the best way to prevent any escalation of tensions.
AIR DEFENCES
Two days after Russian air raids killed 19 people in Ukraine, wounded more than 100 and knocked out power supplies across the country, Stoltenberg urged allies to provide additional air defence systems for Ukraine.
Advanced air defence systems are designed to protect entire cities from air attacks.
Stoltenberg called Russia's missile attacks a sign of weakness and a result of the fact that President Vladimir Putin was running out of alternatives.
"The reality is that they're not able to make progress on the battlefield. Russia is actually losing on the battlefield," Stoltenberg said.
"Ukraine has the momentum and continues to make significant gains, while Russia is increasingly resorting to horrific and indiscriminate attacks on civilians and critical infrastructure."
On Tuesday, Ukraine received the first of four IRIS-T SLM air defence systems Germany promised to supply, a German defence ministry source said.
A senior US defence official, speaking on condition of anonymity, said Germany's IRIS-T system was another sign of the commitment to provide air defences to Ukraine, predating Putin's latest missile strikes on the country.
"Again this is a horrible set of circumstances, what's occurred," the official said. "But the fact that Russia has this capability and is willing to use that capability, including against civilian infrastructure and civilian targets, is not a surprise."
Moscow, which calls its actions in Ukraine a "special military operation" to eliminate dangerous nationalists and protect Russian-speakers, has accused the West of escalating the conflict by supporting Kyiv.
Before NATO defence ministers kick of their talks with a dinner on Wednesday, they are set to meet with partners of the Ukraine Contact Group, a body established on the initiative of the United States to keep up arms supplies to Kyiv.
Discussions of the more than 50 countries would focus on providing additional air defence systems to Ukraine, said the US ambassador to NATO, Julianne Smith.
Ukraine's Defence Minister Oleksii Reznikov will take part in both Brussels events.