Russia is retaining a temporary ceasefire in humanitarian corridors in Ukraine, head of the Russian National Defense Control Center Col. Gen. Mikhail Mizintsev alleged on Wednesday.

Ten of the corridors were proposed by Moscow, while three were proposed by Kyiv, Mizintsev told reporters at a press briefing.

"Today, at exactly 10 a.m. local time, in accordance with agreements reached on 10 humanitarian corridors initiated by the Russian Federation and three more at the request of the Ukrainian side, the Russian Armed Forces introduced a temporary ceasefire, which is being strictly observed until now," Mizintsev said

No practical measures for the preparation of humanitarian convoys have been carried out so far, and no one has ever arrived at the humanitarian corridors that have been opened, Mizintsev said. The formation of organized humanitarian convoys has also not been recorded, he claimed.

A devastating Russian airstrike has destroyed a maternity and children’s hospital in the besieged Ukrainian city of Mariupol, according to Ukrainian officials.

Ukraine’s president Volodymyr Zelenskyy and local officials have posted videos on social media of what appears to be the devastated hospital, partly caved in and with walls blown out, the grounds littered with burnt-out vehicles.

ABC News is attempting to independently verify the attack.

Ukrainian authorities have said there are casualties and Zelenskyy wrote that there are children under the rubble.

Ukrainian officials have accused Russia of deliberately targeting the hospital.

Pavlo Kirilenko, the head of the Donetsk regional military administration, wrote on Facebook that a Russian aircraft targeted the hospital. Other officials have suggested there were multiple strikes.

Zelenskyy has called it an “atrocity” and called on the international community again to impose a "no-fly" zone.

"Direct strike of Russian troops at the maternity hospital. People, children are under the wreckage. Atrocity! How much longer will the world be an accomplice ignoring terror? Close the sky right now! Stop the killings! You have power but you seem to be losing humanity,” Zelenskyy tweeted.

A Russian Defense Ministry spokesman claimed Wednesday that Russia's Aerospace Forces have destroyed more than half of the Ukrainian Armed Forces aircraft.

Russian Defense Ministry spokesman Igor Konashenkov said Russian forces have 89 Ukrainian combat planes and 57 helicopters out of an estimated total of 250 combat aircraft once in possession of the Ukrainian Armed Forces and "in good working order" prior to Russia's special military operation in Ukraine.

"Ninety percent of Ukrainian military airfields, which accommodate the core combat aviation force, have been rendered inoperable," Konashenkov said.

He said that as of Wednesday, Russia has observed "only isolated attempts" of the Ukrainian Air Force's combat aircraft to take off.

Neither U.S. Defense officials nor Ukrainian officials has confirmed Konashenkov's report.

The United States said it's sending two Patriot anti-missile batteries stationed in Europe to Poland as a "defensive deployment" at the request of the Polish government.

While testifying before Congress Tuesday on Russia's invasion of Ukraine, U.S. Under Secretary of State for Political Affairs Victoria Nuland said there were discussions underway with the Polish government about a possible deployment of Patriot batteries. The U.S. military's European Command (EUCOM) later confirmed that two batteries already in Europe would be deployed to Poland.

"At the direction of the Secretary of Defense and at the invitation of our Polish allies, General Wolters, Commander of U.S. European Command, has directed U.S. Army Europe and Africa to reposition two Patriot Batteries to Poland," EUCOM spokesman Capt. Adam Miller said in a statement Tuesday. "This defensive deployment is being conducted proactively to counter any potential threat to U.S. and Allied forces and NATO territory. This is a prudent force protection measure that underpins our commitment to Article Five and will in no way support any offensive operations. Every step we take is intended to deter aggression and reassure our Allies."

The move came hours after the U.S. dismissed Poland's offer to transfer all of its MiG-29 fighter jets to a U.S. air base in Germany to boost Ukraine's fight against Russia, with Pentagon press secretary John Kirby saying in a statement Tuesday that "we do not believe Poland's proposal is a tenable one."

Poland is expecting delivery later this year of two Patriot batteries it had bought in 2018. The air defense systems are intended to shoot down incoming missiles, so their deployment to Poland means there are concerns about dealing with any incoming missile fire into the country, which shares a 330-mile border with Ukraine. It was unclear exactly where in Poland the Patriot batteries would be placed.

-ABC News' Luis Martinez