REHOBOTH BEACH, Del. — The Biden administration will rush advanced air defense missiles to Ukraine by delaying certain weapons shipments to other countries, a move that a White House spokesperson described Thursday as “difficult but necessary” given Russian advances in the war.

The spokesperson, John Kirby, said Ukraine had a critical need for Patriot interceptor missiles now that Russia has accelerated attacks against cities and civilian infrastructure in Ukraine. He did not name the other countries affected but said the decision would not apply to weapons shipments to Israel or Taiwan.

“The broader message here to Russia is clear,” Kirby told reporters. “If you think you’re going to be able to outlast Ukraine, and if you think you’re going to be able to outlast those of us who are supporting Ukraine, you’re just flat-out wrong.”

Russia and Ukraine are in their third year of war, with no clear path to military victory. The two countries increasingly are fighting a war of attrition, firing thousands of artillery shells, missiles and rockets every day.

The Patriot missiles will be crucial as Ukraine tries to improve its air defenses, particularly when it comes to its power grid and other infrastructure, which Russia has been pummeling. The weapon is the most advanced Western air defense system provided to Ukraine thus far and shoots down Russian ballistic missiles and warplanes at ranges of about 40 and 70 miles, respectively.

About a half-dozen countries in the Middle East and Europe are buying Patriot missiles from the United States, said Tom Karako, director of the Missile Defense Project at the Center for Strategic and International Studies in Washington.

The White House’s announcement was a reminder of the extraordinary demand for air defense capacity and production, he said.

“Borrowing from Peter to pay Paul is never a fun choice,” Karako added.

Kirby said the shipments to Ukraine would be “in the realm of hundreds” and take place in the coming weeks. President Volodymyr Zelenskyy of Ukraine has made clear that his country was in “desperate” need of additional air defenses, Kirby said.

The White House’s decision will also speed deliveries of missiles to Ukraine for use in the National Advanced Surface-to-Air Missile System, or NASAMS, which is produced by the United States and Norway. While less capable than the Patriot, NASAMS has been heavily used to defend key infrastructure sites in Ukraine. Its ammunition is far more plentiful in stockpiles of NATO member states.

The time frame on delayed shipments to other countries varied based on their individual contracts, Kirby said. The United States had notified allies of the delays, and many were “fully supportive” of the move.

The announcement comes as the Biden administration has ramped up efforts in recent weeks to blunt Russia’s efforts to bolster its military.

On Wednesday, President Vladmir Putin of Russia visited North Korea, where he and Kim Jong Un, the North’s leader, agreed that if one country found itself in a state of war, then the other would provide “military and other assistance with all means in its possession without delay,” according to the text of the agreement.

Kirby said the pact was a sign of Russia’s desperation.

“They don’t have a lot of friends in the world, and they’re trying to do everything they can to pull on the strings of the friends that they do have,” he said. “Russia’s absolutely isolated on the world stage; they’ve been forced to rely again on countries like North Korea and Iran.”

South Korea said Thursday that it would consider sending arms to Ukraine, a major policy change that was suggested after Russia and North Korea rattled the region and beyond by signing the mutual defense pact.

The office of South Korean President Yoon Suk Yeol issued a statement condemning the agreement, calling it a threat to his country’s security and a violation of U.N. Security Council resolutions, and warned that it would have negative consequences on Seoul’s relations with Moscow.

South Korea, a growing arms exporter with a well-equipped military backed by the United States, has provided humanitarian aid and other support to Ukraine, while joining U.S.-led economic sanctions against Moscow. But it hasn’t directly provided arms to Kyiv, citing a long-standing policy of not supplying weapons to countries actively engaged in conflict.

Associated Press contributed.