New Delhi, Dec. 4 -- NATO Secretary-General Mark Rutte brushed off fresh concern Tuesday about the United States' commitment to the military organization on the eve of a meeting of allied foreign ministers focused on Russia's war against Ukraine.

U.S. Secretary of State Marco Rubio was expected to miss Wednesday's meeting, which will unfold during high-stakes negotiations in Moscow and in Europe about Ukraine's future. His rare absence at the American-led alliance comes after President Donald Trump's 28-point proposal to end the almost four-year war dismayed European allies and Canada last month.

At a pivotal moment in NATO's history, European allies see Russia's invasion as an existential threat, and senior officials have warned that R...