The United States said Tuesday it was "not encouraging" Ukraine to strike into Russia after drone attacks on bases widely seen as carried out by Kyiv.

"We are not enabling Ukraine to strike beyond its borders; we are not encouraging Ukraine to strike beyond its borders," State Department spokesman Ned Price told reporters.

"Everything we are doing -- everything the world is doing to support Ukraine -- is in support of Ukraine's independence," he said.

He stopped short of attributing the drone attacks to Ukraine, which has not claimed responsibility. Russia said three people were killed and two aircraft damaged in the attacks Monday on three bases deep into its territory.

Experts believe Ukraine penetrated Russian airspace with simple Soviet-era drones and not any of the billions of dollars in military assistance given by Western powers since Moscow's February 24 invasion.

"We are providing Ukraine with what it needs to use on its sovereign territory -- on Ukrainian soil -- to take on Russian aggressors," Price said.

Price also declined comment on a Wall Street Journal report that the United States has altered HIMARS sent to Ukraine -- a rocket system seen as a game-changer on the battlefield -- to prevent firing into Russia.

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President Joe Biden has publicly said he does not support longer-range missile capacities for Ukraine, fearing an escalation that would pit the United States more directly against Russia.