Russian President Vladimir Putin on Tuesday announced that he is suspending the country’s participation in the 2010 START treaty nuclear arms reduction treaty with the US. His announcement followed President Joe Biden’s visit to Ukraine, where the Democratic Party leader promised additional support.

Biden responded to Putin’s state of the nation address by asking the Russian President to ‘end the war’ against Ukraine. Talking from Warsaw, Poland, he said the US and its allies will continue to support Ukraine and push for new sanctions on the Kremlin.

The New Strategic Arms Reduction Treaty – START – puts a cap on the US and Russia’s strategic nuclear warheads, long-range bombers and missiles. It also allows each nation to inspect the other’s nuclear sites 18 times a year to ensure compliance with the pact.

Tactical nuclear weapons are designed to be used on the battlefield. Strategic ones, which are bigger, are carried on intercontinental ballistic missiles to be used on much larger target areas.

A look at Russia and the United States’ nuclear stockpile:

Nine countries have tactical nuclear weapons, according to the Federation of American Scientists. They are Russia, the United States, China, France, the United Kingdom, Pakistan, India, Israel and North Korea.

Russia has a stockpile of an estimated 2000 tactical nuclear missiles, the Bulletin of the Atomic Scientists states. The U.S. has an estimated 200 tactical nuclear bombs.

Russia and the United States together hold 90% of the world’s nuclear warheads.

“One year ago, the world was bracing for the fall of Kyiv,” Biden said on Tuesday. “Well, I just came from Kyiv and I can report Kyiv stands strong. Kyiv stands proud. Kyiv stands tall. And most importantly, Kyiv stands free.”

“One year into this war, Putin no longer doubts the strength of our coalition, but he still doubts our conviction; he doubts our staying power; he doubts our continued support for Ukraine; he doubts they can remain unified,” Biden said. “But there should be no doubt — our support for Ukraine will not waiver. NATO will not be divided and we will not tire.”