NATO ambassadors will hold an emergency meeting at 1000 CET (0900 GMT) on Wednesday to discuss a missile strike in eastern Poland close to the Ukrainian border that killed two people on Tuesday, two NATO officials and a European diplomat said.
The Brussels gathering will be chaired by Secretary-General Jens Stoltenberg, who will hold a news conference around 1230 CET, NATO said, amid concerns that the incident could be a trigger for the Ukraine war to spill into neighbouring countries.
NATO member Poland said the rocket landed on a grains facility in a village about 6 km (4 miles) from the border.
NATO allies were quick to express concern and support.
"The reaction of our allies, their unequivocal support and willingness to stand by us, shows that we are a much safer country than if we were not in NATO," Poland's deputy foreign minister Pawel Jablonski told private radio station RMF FM on Wednesday.
"As a country bordering Ukraine, we may be exposed to various types of incidents, including accidental ones," he added.
Many allies called for thorough investigations on the rocket's source. U.S. President Joe Biden said it was probably not fired from Russia. Russia, meanwhile, said it had nothing to do with the blast.
But it were to be determined that Moscow was to blame for the blast, it could trigger NATO's principle of collective defence known as Article 5, in which an attack on one of the Western alliance's members is deemed an attack on all, starting deliberations on a potential military response.
In the meantime, Poland will likely invoke NATO's Article 4 , Polish officials said in the early hours of Wednesday.
The article 4 is a call for consultations among the allies in the face of a security threat, allowing for more time to determine what steps to take.
The explosion near the Ukrainian border came as Russia unleashed a wave of missiles targeting Ukrainian energy infrastructure, attacks that Kyiv said were the heaviest in nearly nine months of war.
NATO and G7 countries said earlier on Wednesday, after meeting in the margins of a G20 leaders' summit in Indonesia, that they would remain in close contact to decide any possible reaction to the blast.
Contacts are also ongoing at European Union level. EU foreign policy chief Josep Borrell tweeted that he had assured Poland of the "EU Foreign Affairs Council' full support" in talks overnight with Polish Foreign Minister Zbigniew Rau.
