April 30 marked 100 days since President Trump took office. US special envoy for Ukraine Keith Kellogg previously set a goal of ending the conflict in the first 100 days.
"We're going to work very hard over the next 100 days to try to bring these guys together," Vance told Fox News in an interview on Wednesday.
However, Vance admitted there is a "very big gulf" between the desires of the Russians and the Ukrainians.
In April, US President Donald Trump said he will "take a pass" on his efforts to broker peace in Ukraine if either party to the conflict stalls peace talks.