Alert Level Raised at U.S. Bases in Europe Over Russian Threats

American defense officials raised the security alert level at military bases in Europe over the weekend in response to vague threats from the Kremlin over Ukraine’s use of long-range weapons on Russian territory, according to U.S. and Western officials.

Officials said that no specific intelligence about possible Russian attacks on American bases had been collected. Any such attack by Russia, whether overt or covert, would be a significant escalation of its war in Ukraine.

Russia has been stepping up acts of sabotage in Europe, hoping to disrupt the flow of matériel to Ukraine. So far, no American bases have been targeted in those attacks, but U.S. officials said raising the alert level would help ensure that service members were keeping watch.

Throughout the war, U.S. officials have assessed that President Vladimir V. Putin is loath to expand the war beyond Ukraine’s borders.

But stepped-up U.S. and European aid — and the easing of restrictions on how that matériel is used — has caused consternation in Moscow, according to American officials. Russia’s recent statements have made some American and European officials wary.

Ukraine has been using longer-range American missiles known as ATACMS to strike deep into occupied Crimea. The United States has also said Ukraine can use them in cross-border attacks on Russian military targets.