By Andrew Higgins and Michael R. Gordon

New York Times News Service

KIEV, Ukraine — Russia escalated tensions with Ukraine to the highest level since its stealthy invasion of Crimea in the spring, sending more than 200 trucks from a long-stalled aid convoy into rebel-held eastern Ukraine on Friday over the objections of Kiev and, NATO said, conducting military operations on Ukrainian territory.

NATO officials said that the Russian military had moved artillery units manned by personnel inside Ukrainian territory in recent days and was using them to fire at Ukrainian forces. Russia has repeatedly denied sending troops or military hardware into Ukraine, just as it denied any link to the unidentified gunmen who paved the way for Moscow’s annexation of Crimea — until President Vladimir Putin stated in April that Russian troops were “of course” involved.

There has been a “major escalation in Russian military involvement in eastern Ukraine since mid-August, including the use of Russian forces,” Secretary-General Anders Fogh Rasmussen of NATO said in a statement. “Russian artillery support — both cross-border and from within Ukraine — is being employed against the Ukrainian armed forces,” Rasmussen added. Russia’s Permanent Mission to NATO, in a statement, accused the alliance of indifference to humanitarian suffering in eastern Ukraine and described its protests over the entry of a Russian aid convoy into Ukraine without Red Cross escorts as “another cynical attempt to cover the crimes of Ukrainian authorities.”

Rasmussen did not say how many Russian artillery pieces had been moved into Ukraine or where they were located, but one Western official said the number of Russian-operated artillery units was “substantial.”

The NATO allegations are based on intelligence reports from several alliance members, Western officials said, and the allegation generally echoed Ukrainian claims in recent days of an expanding Russian military involvement in support of pro-Russian rebels who are battling to hold off a Ukrainian offensive.

A NATO spokeswoman, Oana Lungescu, also said the alliance had received multiple reports of the direct involvement of Russian airborne, air defense and special operations forces in Eastern Ukraine.

In a news briefing, the Pentagon spokesman, Rear Adm. John Kirby, condemned the convoy as an “unauthorized entry into Ukraine” and called for the vehicles’ immediate withdrawal. The move into Ukraine, without the Red Cross escorts that had been agreed upon, drew angry accusations from Ukraine that Moscow had broken its word and mounted what Valentyn Nalyvaichenko, the head of Ukraine’s Security Service, called a “direct invasion.”