Ukraine has begun using longer-range ballistic missiles against Russia that were secretly provided by the US, American officials have confirmed.
The weapons were sent as part of a previous US support package, and arrived this month. Officials said they were not announced publicly to maintain Ukraine's "operational security".
They have already been used at least once to strike Russian targets in occupied Crimea.
Further US aid is now heading to Kyiv.
More American weaponry is expected to be sent imminently, after President Joe Biden signed off on Wednesday a new package of economic and military support for Ukraine worth $61bn (£49bn).
The missiles that have already been quietly provided are the longer-range version of the Army Tactical Missile Systems (ATACMS), a state department spokesman confirmed on Wednesday.
The US previously supplied Ukraine with a mid-range version of the ATACMS, but had resisted sending anything more powerful, partly over concerns about compromising US military readiness.
Officials were also concerned that the Ukrainians could use the weaponry to strike inside Russian territory, causing the conflict to escalate, according to NBC, which first reported the news.
The Ukrainians have long called for the systems, which can fire missiles up to 300km (186 miles). Mr Biden is said to have secretly given the green light in February.
Briefing reporters on Wednesday, the state department spokesman confirmed that the provision of the longer-range ATACMS had been "at the president's direct direction".
The US "did not announce this at the onset in order to maintain operational security for Ukraine at their request", Vedant Patel explained.
It is not clear how many of the weapons have already been sent, but US National Security Advisor Jake Sullivan said Washington planned to send more.
"They will make a difference. But as I've said before at this podium... there is no silver bullet," he said.