Russia continued its assault on Ukraine's infrastructure in Kyiv with a swarm of explosive drones throughout Monday morning.

Russia's attacks on Kyiv have been relentless since New Year's Eve. Russia followed up its holiday missile attack with drones that flew into the city just after midnight on Monday morning. Air-raid sirens blared and at least two explosions were heard in the heart of Kyiv, according to The New York Times.

Russia has made relentless use of the Iranian-made Shahed-136 drones since the fall. The drones have an extensive range and explode on impact.

Ukrainian air defenses routinely shoot down most of the drones on approach to their targets, the sheer volume of strikes allows some to detonate.

MULTIPLE EXPLOSIONS ROCK EASTERN UKRAINE CITY OF KHARKIV

Ukraine largely uses U.S.-supplied anti-air defenses to protect its major cities. The U.S. has granted tens of billions of dollars in military aid to the country.

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The flow of weapons has put a strain on U.S. stockpiles, and Congress passed a massive budget granting the Pentagon nearly $900 billion to refit.

The traditional measure of U.S. military readiness has been its capacity to supply and carry out two major conflicts in separate areas of the globe. White House national security adviser Jake Sullivan argued in December that U.S. support for Ukraine has revealed weaknesses in that readiness.

"We went through six years of Stingers in 10 months," Raytheon CEO Greg Hayes told NYT. "So it will take us multiple years to restock and replenish."

The U.S. has sent nearly $20 billion in military aid to Ukraine since February, and there are plans to send much more. The aid is such that President Biden's administration is struggling to keep track of how the aid is being used. The volume of U.S. aid to the country has given rise to some skeptics within the Republican Party, who are calling for greater accountability.