What we know about the missile blast in Poland so far?

A missile blast in NATO-member Poland that Ukraine blamed on Russia raised fears of a deeper confrontation between the US.-led military alliance and Russia amid the deadliest war in Europe since World War Two.

US President Joe Biden said the missile, which killed two people, was probably not fired from Russia and Moscow said it had not targeted the area. Many NATO allies called for thorough investigations and the alliance convened an emergency meeting.

What do we know - and what do we not know?

First news of the incident was reported by Polish Radio ZET which said on Tuesday that two stray missiles hit Przewodow, a village in eastern Poland about 6 km (3.5 miles) from the border with Ukraine.

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According to the Polish foreign ministry, a Russian-made missile fell on the village at 3:40 p.m. local time (0240 GMT) after a massive day of Russian shelling of Ukraine.

A resident who declined to be identified said the two men who were killed were near the weighing area of a grain facility.

Polish President Andrzej Duda said later that, "it was most likely a Russian-made missile," but that the incident was still under investigation. Duda added that "what happened in Przewodów was a one-off event" and "there is no indication that any more will take place".

Duda said he had informed NATO Secretary General Jens Stoltenberg and Biden that it is "highly probable" that the Polish ambassador to NATO "will request to invoke Article 4, that is consultations among the allies."

He also said Poland has no conclusive evidence showing who fired the missile.

It is still unclear what missile struck the village. Russia denied its missiles struck Poland.

"Statements by Polish media and officials about 'Russian' missiles allegedly falling in the area of the settlement of Przewodow are a deliberate provocation aimed at escalating the situation," the defence ministry said.

"No strikes on targets near the Ukrainian-Polish state border were made by Russian means of destruction.

"The wreckage published by Polish media in hot pursuit from the scene in the settlement of Przewodow has nothing to do with Russian weapons."

It was unclear if Russia had used a Cold War hotline - installed after the 1962 Cuban Missile Crisis - to speak to Washington to calm the situation. President Vladimir Putin has yet to comment on the incident.

The United States and its NATO allies are investigating the blast that killed two people in Poland, but early information suggests it may not have been caused by a missile fired from Russia, U.S. President Joe Biden said.

Asked whether it was too early to say that any missile was fired from Russia, Biden said that the trajectory suggested otherwise.

"There is preliminary information that contests that," he told reporters. "I don't want to say that until we completely investigate it but it is unlikely ... that it was fired from Russia, but we'll see."

Associated Press first reported that a senior US intelligence official said Russian missiles crossed into Poland, killing two people.

But later, AP published a different story saying that initial findings suggested that the missile that hit Poland was fired by Ukrainian forces at an incoming Russian missile.

Ukraine blamed Russia.

President Volodymyr Zelenskiy said on Tuesday, without producing evidence, that Russian missiles had hit Poland, a NATO country, in what he called a "significant escalation" of the conflict.

"Russian missiles hit Poland, the territory of our friendly country. People died," Zelenskiy said in his nightly video address.

"The longer Russia feels impunity, the more threats there will be to anyone within reach of Russian missiles. To fire missiles at NATO territory! This is a Russian missile attack on collective security! This is a very significant escalation. We must act," he said.

NATO will hold an emergency meeting at 10.00 CET (0900 GMT) on Wednesday to discuss the explosion, two NATO officials and a European diplomat said.

The gathering of NATO ambassadors in Brussels will be chaired by Secretary-General Stoltenberg, who will hold a news conference around 12.30 CET, NATO said in a statement.