MOSCOW - Russian officials lashed out at the West yesterday, excoriating NATO for expelling two Russians suspected of spying and for pushing ahead with planned military exercises in Georgia.

In sharp contrast to the Obama administration's call for a "reset" of U.S.-Russian relations and the recent thaw in Russian-NATO ties, it was a day of acrimony and veiled threats as Russian officials resorted to some of their toughest talk in weeks.

Two high-ranking members of Russia's permanent mission to NATO were stripped of their credentials and expelled from Belgium on accusations of espionage, the alliance's leadership announced yesterday. The two were identified as political desk chief Viktor Kochukov and mission attache and executive secretary Vasily Chizhov.

The Russian Foreign Ministry called the expulsions "provocative" and issued a statement warning NATO to "think about the consequences of what happened."

NATO suspended political contact after troops crossed into Georgia last summer - provoked, Russia said, by a Georgian assault on the breakaway republic of South Ossetia.

Wednesday marked the first day of renewed political discussion between the two sides. But the talks came amid increased tension over NATO plans to hold military exercises in Georgia next week.

The exercises were scheduled long before last year's war, but Russian officials argue that they constitute a potentially destabilizing threat.

Russian President Dmitry A. Medvedev yesterday called the exercises "an open provocation."

Against the background of rippling tensions, Russia signed a treaty accepting responsibility for military control of the so-called borders dividing Georgia's rebel republics with the rest of the Caucasian nation.

Last summer's war revolved around South Ossetia and Abkhazia, another republic that has broken with Georgia. Russia since has recognized the two areas as independent countries.

The presidents of the two republics were in Moscow on yesterday to sign the agreement with Medvedev. The treaty gives Russia responsibility for guarding the cease-fire line until the two rebel territories create their own border guard.