February 21, 2024

Russia has rebuilt its own domestic supply of cruise missiles, and shorter-range missiles and artillery, despite Western financial sanctions and export controls. But to keep up with the intensity of the barrage against Ukraine, it has been turning to North Korea and Iran. Mr. Kirby said that the range of the missiles now being shipped from North Korea meant that they could be launched from well inside Russia — where launch sites are harder for Ukraine to hit — and still reach a number of Ukrainian cities.

The technology North Korea is seeking includes fighter jets and ballistic-missile launch technology, Mr. Kirby said. Other American officials have reported that the North is also seeking more help on the range and accuracy of its intercontinental ballistic missiles, which it has repeatedly tested in recent months. But it is not clear whether Russia has agreed to further help the North on these nuclear-capable missiles. In the past, North Korea has relied heavily on what appeared to be Russian missile designs, but it has never been clear how closely it has worked with Russian engineers.

The Biden administration has pressed lawmakers on Capitol Hill to provide $50 billion more to Ukraine to help fund its military operations this year. Republican opposition has been growing, with party leaders saying they will support additional aid only if the Biden administration makes significant concessions on border policy.

Mr. Kirby, speaking at the White House, made the case on Thursday that the missile shipments to Russia underscored the need to pass new aid to the Ukrainians. The White House contends there is virtually nothing left from last year’s arms packages. And Mr. Kirby contended that American credibility was at stake.

“Do you know who else is watching? Vladimir Putin, and President Xi in Beijing,” he said. “They are watching to see whether or not the United States really will prove to be a reliable partner.”