Lloyd Austin made the statement at a virtual meeting of the Ukraine Defense Contact Group, a group of over 50 countries that support Ukraine, on Wednesday.
The Pentagon chief said: "I'm proud that this history-making Contact Group has committed more than USD 80 billion in security assistance to Ukraine since the Kremlin launched its indefensible invasion."
Austin added that Russia "cannot outlast us or prevail in a contest of wills."
He declared that allies would help Ukraine "fight through this winter and defend its critical infrastructure" and urged countries to "provide Ukraine with air-defense capabilities to protect its people."
The US defense secretary also reiterated that the West would "stand with Ukraine for as long as it takes."
Meanwhile, 20 countries led by Germany and France pledged to take measures to strengthen Ukraine's anti-aircraft and anti-missile forces, public broadcaster Polish Radio's IAR news agency reported.
Ukraine's President Volodymyr Zelensky welcomed the move, saying he was "grateful to every country that participates in these efforts, which enable our cities and villages to be more protected from Russian attacks."
Speaking in a televised address to the nation, Zelensky added that "Ukraine's sky shield" was "getting more powerful" every month.
Wednesday's virtual gathering was the 17th meeting of the Ukraine Defense Contact Group, which was established in April last year to coordinate international security assistance for Kyiv amid Russia's invasion, Polish state news agency PAP reported.
Thursday is day 638 of Russia’s war on Ukraine.
Russia invaded Ukraine on February 24, 2022, launching the largest military campaign in Europe since World War II.
Source: IAR, PAP, president.gov.ua, defense.gov