During the week, Ukraine and Russia have accused each other of the escalating violence between government forces and Moscow-backed insurgents in eastern Ukraine.
According to Ukrainian President Volodymyr Zelenskyj, 20 Ukrainian soldiers have been killed and 57 injured since the beginning of the year.
"Ongoing aggression"
On Friday, US President Joe Biden spoke with Zelensky and shortly afterwards a statement came from the White House:
"President Biden underlines the United States' unwavering support for Ukraine's sovereignty and territorial integrity in the light of Russia's ongoing aggression in the Donbas and Crimea."
A statement from the US State Department said that the US forces in Europe had increased their preparedness.
The conflict between Ukraine and the Moscow-backed separatists has been going on since 2014, and during the past week violence has intensified again in eastern Ukraine, despite the parties concluding a ceasefire agreement last year.
"Respond"
For example, there have been reports of increased Russian military activity on the Russian-annexed Ukrainian Crimean peninsula and in border areas near Ukrainian areas of Donetsk and Luhansk, which are controlled by separatists.
Kremlin spokesman Dmitry Peskov counters that Russia will be forced to "respond" if the United States were to send troops to Ukraine.
Kiev calls for a joint military exercise with NATO to create stability in the region.