The attacks came ahead of another round of U.S.-brokered talks between envoys from Russia and Ukraine on Tuesday and Wednesday in Geneva, just before the fourth anniversary of the all-out Russian invasion of its neighbor on Feb. 22.
Speaking at the Munich Security Conference in Germany on Saturday, Ukrainian President Volodymyr Zelenskyy suggested there were still questions remaining over future security guarantees for his country. Zelenskyy also questioned how the concept of a free trade zone - proposed by the U.S. - would work in the Donbas region, which Russia insists Kyiv must give up for peace.
He said the Americans want peace as quickly as possible and that the U.S. team wants to sign all the agreements on Ukraine at the same time, whereas Ukraine wants guarantees for the country's future security signed first.
Zelenskyy's concerns were echoed by Sen. Jeanne Shaheen, a ranking member of the U.S. Senate Foreign Relations Committee.
"Unless we have real security guarantees on whatever peace agreement is ultimately determined, we are going to be here again, because one of the things we know is that Russia has geared up not just for Ukraine, but to go beyond Ukraine," she told reporters in Munich on Sunday.