More NATO countries will move troops and fighter jets eastwards after more than a dozen drones entered Polish airspace on Wednesday.
Denmark, France and Germany have joined a new mission to bolster the military alliance's eastern flank. Other NATO allies are expected to take part later.
Tensions have been high across Europe since Poland accused Russia of an unprecedented incursion. Some of the 19 drones that entered Polish territory were shot down, while others crashed into fields and even a house in eastern Poland.
Warsaw said the incursion was deliberate, but Moscow downplayed the incident, saying it had no plans to target facilities in Poland.
Drones and missiles have occasionally veered into countries bordering Ukraine, including Poland, during Russia's full-scale invasion - but this was the most serious incident of its kind since the war began in February 2022.
Polish Prime Minister Donald Tusk described the situation as the closest we have been to open conflict since World War Two.
Despite the provocations, Moscow has dismissed the allegations of aggression, prompting NATO allies such as Denmark to strengthen their military assets in the region. Denmark will contribute two F-16 fighter jets and a warship, with other nations like France and Germany also deploying advanced aircraft to enhance security.
On Friday, during a UN Security Council session, US officials reaffirmed their support for Poland and NATO, emphasizing the commitment to defend all alliance territories against such violations.
As diplomatic tensions continue to escalate, the situation remains precarious with ongoing discussions about security measures and military preparedness in Eastern Europe.
