He told this to journalists in New York on Tuesday, Ukrinform reports, citing Sky News.
According to him, the Ukraine war is "a war of attrition" but has not reached a stalemate.
Kyiv urgently needs further supplies of air defenses, including ammunition, spare parts and maintenance for the systems the Ukrainian military already has, Stoltenberg said.
"We see that air defense is saving lives every day in Ukraine," he said.
He cited recent Ukrainian gains in its counteroffensive as evidence a stalemate had not been reached - and urged the West to continue its military, humanitarian and financial aid to Ukraine.
"If we want an end to the war, if we want a just and lasting peace, then military support to Ukraine is the right way. We are ready for the long haul," Stoltenberg said.
In his opinion, a message should be sent to the Kremlin that "President Putin cannot wait us out."