The White House urged Moscow on Friday to stop its "extremely dangerous and provocative" attempts to destabilize Ukraine, where tensions have soared again in the past 24 hours.
There has been an "escalation" in Russian activity in recent weeks to unsettle the already tense situation on the ground in eastern Ukraine, National Security Council spokeswoman Caitlin Hayden said in a statement.
Earlier, Ukraine said it had destroyed part of a Russian armored column that entered onto its territory in an incursion that sent cross-border tensions rocketing.
Russia and neighbouring Ukraine have been wrangling for days over a convoy that Moscow says is carrying humanitarian aid for besieged rebel-held cities but which Kiev suspects could be a "Trojan horse" to provide military help to the insurgents.
"Even as we work to gather information (about the partial destruction of the Russian armored column), we reiterate our concern about repeated Russian and Russian-supported incursions into Ukraine," Hayden said.
"Russia has no right to send vehicles, persons, or cargo of any kind into Ukraine, under any pretext, without the government of Ukraine's permission." Hayden warned that "the escalation in Russian activity designed to destabilize Ukraine in recent weeks is extremely dangerous and provocative." "It includes supplying separatist fighters with tanks, armored vehicles, artillery and multiple rocket launchers (MRLs)," she added.
Russia has also been firing artillery and rockets from Russian territory into Ukraine "on a regular basis," said Hayden.
Moscow has consistently denied supporting rebels in eastern Ukraine and the crisis has led to tit-for-tat sanctions between the West and Russia over Moscow's alleged behaviour.
NATO separately also accused Russia of active involvement in the "destabilization" of eastern Ukraine, where pro-Kremlin separatists have been fighting against Kiev for four months.
Russian President Vladimir Putin can help put a stop to the conflict "by ending Russian firing into Ukraine; stopping its supply of weapons, support and cash to separatists; and closing the border to militants, including by facilitating an effective border monitoring mission under the auspices of the OSCE," said Hayden.
"The continued Russian military intervention into Ukraine is entirely at odds with legitimate efforts to provide humanitarian assistance and negotiate a peaceful resolution to the overall crisis."