The Defense Department assesses that the Ukrainians still have a majority of their air defense systems available to them, the official said.
"[The Ukrainians] have been clear that they want to boost their inventories for air defense capabilities. They've been clear that they want more aircraft. … We're talking to allies and partners about doing what we can to help them get more long-range air defense systems," the official said.
Regarding the U.S.-made Switchblade unmanned aerial systems, a significant number of them are now inside Ukraine for use by their forces, the official said.
These UAS can carry explosives and have onboard cameras, videos and sensors. The official noted that operating the Switchblade requires only about a day or two of training.
Most of the $800 million in U.S. arms have already been delivered to the Ukrainians, the official said. The Pentagon is also working on another $100 million for Javelin missiles.
"These items are not sitting around very long. … We talk to them very frequently about their needs. And, not just at the secretary's level but below that, to get a sense of what they want. And then we try to coordinate the delivery of that stuff, not just from us, but other nations, and get them on trucks as fast as we can," the official added.
Thus far, the Russians have launched about 1,540 missiles. Russian airstrikes continue to be focused on Mariupol, Ukraine, and the joint force operation area there and to the east in the Donbas region.
The Russian convoy is still about 60 kilometers north of Izyum, Ukraine, the official said. "We do assess that it's moving, but not at breakneck speed."
It likely includes some command and control elements and some enablers, the official said. "We think it's also intended for resupply – perhaps an effort to amend their poor performance in logistics and sustainment in the north."
There is still heavy fighting around Izyum right now.
More Russian forces are located about 20 kilometers south of Izyum, but those forces haven't been advancing toward the city in any significant manner thus far, the official said.
The Pentagon is aware of reports that chemical weapons were used in Mariupol, the official said. "We cannot confirm the use of chemical agents at this time. We're still evaluating."