Jake Sullivan made the statement on Friday, following talks with the head of Poland's National Security Bureau (BBN) Jacek Siewiera, the White House said.
America's national security advisor "expressed the United States’ solidarity with Poland, our close NATO Ally, as it deals with reports of a missile temporarily entering Polish airspace," according to officials.
Sullivan also "pledged technical assistance as needed and assured his Polish counterpart that President Biden is following this issue closely."
Meanwhile, Poland's Siewiera "expressed appreciation for U.S. support, and they stated their governments will remain in close contact," the White House said.
NATO Secretary General Jens Stoltenberg, who earlier spoke to Polish President Andrzej Duda about the "incursion into Polish airspace," said the Western alliance "stands in solidarity with our valued ally" over the missile incident in Poland.
Earlier in the day, Poland's leaders including the president, Prime Minister Donald Tusk, military chiefs and top security officials held urgent talks, after the Polish Army said that on Friday morning an "unidentified air object has flown into Polish airspace from the direction of the Ukraine border, and was monitored by air defences until its signal died down."
On Friday afternoon, the General Staff of the Polish Armed Forces said in a statement that "an object violated Polish airspace at 7:12 a.m. local time from the direction of the border with Ukraine, before leaving Poland's territory after less than three minutes."
The object was a "Russian cruise missile," military officials added.
The missile's trajectory was followed by Polish and allied radiolocation systems, while the Polish army also put "air defences on standby" and "dispatched F-16 fighter jets" to patrol the area where the missile crossed into Polish airspace, among other measures, the General Staff in Warsaw said.
The Polish army added further information would be provided as it is established.
It came as Russia on Friday morning fired 158 missiles against Ukrainian cities, including Kyiv, Odesa and Lviv, killing at least twelve people and injuring 76, and also struck a critical infrastructure facility in the Lviv region which borders Poland, according to news outlets.
The defence ministry in Kyiv said it was Russia's "most massive air attack" since it invaded Ukraine in February 2022.
Friday is day 674 of Russia’s war on Ukraine.
Russia invaded Ukraine on February 24, 2022, launching the largest military campaign in Europe since World War II.
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Source: PAP, Interia.pl, White House