The United States has rejected claims by Russia that Ukraine is now operating bio warfare labs with US support. The White House warns that Russia could use the allegation as a pretext to resort to using chemical weapons.

Russian Foreign Ministry spokesperson Maria Zakharova said on Wednesday, "We have confirmed during our special military operation in Ukraine documents showing there was an attempt to erase military biological programs by the Kyiv regime. They were carried out by Kyiv and financed by the United States of America."

Zakharova demanded transparency from Washington but did not provide any details of the alleged documents.

White House Press Secretary Jen Psaki calls the charge preposterous. She tweeted, "This is all an obvious ploy by Russia to try to justify its further premeditated, unprovoked, and unjustified attack on Ukraine."

She also said, "We should all be on the lookout for Russia to possibly use chemical or biological weapons in Ukraine, or to create a false flag operation using them."

A senior US Defense Department official said on Wednesday that Russian troops are firing missiles and bombs on targets in Ukraine relentlessly. The official said more than 710 missiles have been launched since the invasion began, most of them from mobile systems deployed within the country and from Russia.

The official also says the Russian military is using unguided bombs that are prone to miss targets and eventually end up increasing damage to civilian infrastructure and causing more civilian casualties.

Amid reports of intensified shelling, international media outlets quote Ukrainian authorities as saying that 17 people were injured when a maternity hospital in the port of Mariupol was hit during a Russian airstrike.

Ukrainian President Volodymyr Zelenskyy tweeted on Wednesday that people, including children, were still under the wreckage.

Zelenskyy said, "How much longer will the world be an accomplice by ignoring terror? Close the skies right now! Stop the killings! You have power but you seem to be losing humanity."
The UN human rights office says that as of March 8, at least 516 civilians, including 37 children, had been killed since the Russian invasion began.

Most of the deaths were caused by missiles and bombs. A total of 908 people have been injured.

The UN refugee agency says by Tuesday, more than 2 million Ukrainians had fled to other countries since the start of the invasion.

The UNHCR says over one million people, or about 60 percent, have gone to Poland, and 200,000 to Hungary, 150,000 to Slovakia and 80,000 each to Romania and Moldova. The UN agency says more than 90,000 have entered Russia.

Washington has flatly refused any plans to provide MiG fighter jets to Ukraine through a second country. Polish leaders had offered to send Soviet-era fighter jets to a US airbase in Germany.

US Defense Department Press Secretary John Kirby said on Wednesday, "The intelligence community has assessed the transfer of MiG-29s to Ukraine may be mistaken as escalatory and could result in significant Russian reaction that might increase the prospects of a military escalation with NATO."

Kirby called it a high-risk venture that would not significantly change the Ukrainian Air Forces' effectiveness.