MOSCOW  Three days after the Czech Republic signed an agreement with the United States to host a tracking radar for an antiballistic missile system that Russia vehemently opposes, the authorities in Prague said the flow of Russian oil to their country was beginning to dwindle.

In a statement on Friday, Czech officials declined to link the reduced supply to the deal signed Tuesday in Prague. Still, though the flow of oil can vary for technical reasons, it was clear that the Czechs suspected a connection and intended to ask the Russians to explain the decline.

Russia maintains that the missiles meant to shoot down other missiles pose a threat to its own nuclear deterrence. The Bush administration says they are intended instead to counter a threat from Iran, which launched nine missiles on Wednesday.

In the deal, the Czech Republic agreed to have the United States place a tracking radar on Czech territory. That radar would be linked to interceptor missiles elsewhere; the United States is in talks with Poland and Lithuania to host those.