A senior aide to U.S. President Barack Obama has said that the United States should reconsider its policy of not providing lethal aid to Ukraine, which is grappling with pro-Russian separatists in the east of the country.
Tony Blinken, the deputy national security adviser, cited "serious violations" by Moscow of the Minsk agreement.
Signed by Russia, Ukraine and rebels from Ukrainian separatist regions of Donetsk and Luhansk on September 5 in the Belarus capital, the agreement imposed a cease-fire and set out steps toward peace.
Blinken said providing Kyiv with lethal military aid may prompt Moscow "to think twice and deter them from further action."
Blinken was speaking on November 19 at a congressional hearing on his nomination to be Obama's deputy secretary of state.
Analysts say providing defensive military equipment to Ukraine has broad support in Congress.
Ukraine accused Russia last week of sending soldiers and weapons to help separatist rebels in eastern Ukraine launch a new offensive in a conflict that has already killed more than 4,100 people.
NATO has accused Russia of sending tanks and troops to eastern Ukraine in recent days to support the separatists.
NATO chief Jens Stoltenberg said on November 18 that there had been a "serious military buildup" both in eastern Ukraine and on the Russian side of the border, and urged Moscow to pull back its forces.
Russia backs the separatists but denies it is directly involved in the conflict.
Blinken's comments come a day ahead of a scheduled two-day visit to Kyiv by U.S. Vice President Joe Biden.
A day after arriving in the Ukrainian capital, Biden is due to meet Ukrainian President Petro Poroshenko and Prime Minister Arseniy Yatsenyuk on November 21.
On November 19, Yatsenyuk rejected a call by Russian Foreign Minister Sergei Lavrov for Kyiv to hold direct talks with the separatists.
Lavrov told the State Duma earlier on November 19 that Kyiv should establish "stable contacts" with the rebels in the regions of Luhansk and Donetsk.
But Yatsenyuk told Moscow to stop "playing games" aimed at legitimizing "terrorists."
Meanwhile, Russian President Vladimir Putin said Moscow was ready for "practical cooperation" with Washington as long as the United States treats Russia as an equal partner and stays out of its internal affairs.
Putin spoke at a ceremony during which he received the credentials of foreign envoys including John Tefft, the new U.S. ambassador to Moscow.
In a statement issued after the ceremony, Tefft said he was committed to maintaining "open and frank lines of communication" with the Russian authorities.
