Deputy spokesperson Marie Harf described the new information as adding to the "preponderance of evidence" that Russia is continuing to provide the separatists with advanced surface-to-air weaponry.
On Wednesday, declassified intelligence analysis and imagery was made public regarding Russia's role in providing the weaponry that shot down Malaysia Airlines Flight 17 on July 17 over restive eastern Ukraine.
On Thursday, Harf announced, "We have new evidence that the Russians intend to deliver heavier and more powerful, multiple rocket launchers to the separatist forces in Ukraine, and have evidence that Russia is firing artillery from within Russia to attack Ukrainian military positions."
That State Department deputy spokesperson explained that the new information was provided by "our intelligence friends," adding that "I can't tell you what the information is based on."
A senior U.S. defense official confirmed that Russia has been firing into Ukraine for "several days."
Pentagon spokesman Col. Steve Warren characterized the artillery fire as "clearly a military escalation" on the part of Russia.
The Russian embassy in Washington, D.C. dismissed the U.S. government's accusations as "unproven allegations."
"If true," former U.S. Ambassador to Moscow Michael McFaul said, "this represents a serious escalation on Putin's part ... Instead of using last week's tragedy as a pretext for ending this war, he seems to be doing the opposite, doubling down."