Ukrainian President Volodymyr Zelensky said he may be willing to compromise on the contested Donbas region, but the economic cost could be high.
"Return to where it all began, and there we will try to solve the issue of Donbas, the complex issue of Donbas," Zelensky called on Russian troops in Ukraine.
Officials in Kyiv said Russian forces had blown up a refinery in Lysychansk owned by Kremlin-controlled oil giant Rosneft.
Former British Army Major Kevin Price said the cold "will degrade the Russian force" and "the Russians are not ready for Arctic conditions."
Ahead of Russia's invasion of Ukraine, President Vladimir Putin repeatedly warned the West about NATO's expansion, viewing it as a threat to Russia's security.
"I voted for peace, not for war," lawmaker Mikhail Matveev tweeted on Friday.
Social media footage shows the military vehicles entering Obolon, directly north of the center of the Ukrainian capital.
The president has already signed an executive action imposing sanctions on two breakaway Ukrainian regions.
The United Nations Security Council will hold an emergency meeting in response to the Russian president's announcement.
The executive order will "provide authority to impose sanctions on any person determined to operate in those areas of Ukraine," Press Secretary Jen Psaki said.
"Russia's decision is yet another example of President Putin's flagrant disrespect for international law and norms," Blinken said in a statement.
Tensions have risen dramatically in eastern Ukraine, with reports of intensifying shelling and fighting between Ukrainian forces and Russian-backed separatists.
Evacuations have been ramped up as shelling in the Russian-backed separatist enclaves of Luhansk and Donetsk has escalated in recent days.
Vladimir Putin is making Russian passports more easily available to Ukrainians living in the self-proclaimed republics of Donetsk and Luhansk, where pro-Kremlin separatists have been battling Kiev forces.
Russia's security chief said that Kiev's reliance on Western support may contribute to Ukraine's loss of statehood.
The Kremlin leader allegedly revealed the news during a closed-door speech on Thursday with top Russian ambassadors.
The U.S. State Department demanded an end to the hostilities as the conflict entered its fifth year.
The Javelin missiles are deemed so effective that intention to sell or deploy them has long warranted a big political announcement.
Moscow claims that any Russian military hardware was looted by rebels from Ukrainian government depots.
The Ukraine had by far the most mine explosions and casualties in the world in 2016 due to ongoing conflict in its eastern region.
U.S. paramedic Joseph Stone is the first casualty of an international monitoring mission in eastern Ukraine.
The OSCE monitor died in a landmine explosion in the region where Russian-backed rebels are fighting Ukrainian forces.
Trump says he "would be surprised" if forces are "uncontrolled" but unsure.
A group considered responsible for U.S. Democratic Party hacks used an Android malware implant to track troops.
Meanwhile Russian interest in east Ukraine has dwindled to a near three-year low.
International observers claim hostilities have increased by 40 percent in a week.