According to the US State Department, the visit aims to "reinforce the strategic value of the United States’ relationships" with the two countries.
Chollet, who is a foreign policy advisor to Secretary of State Antony Blinken, is scheduled to be in Kiev on Tuesday and Wednesday and then travel to Warsaw for a three-day visit beginning on Wednesday.
"He will continue our diplomatic conversations with Ukraine and Poland on a range of issues, including our shared concerns about the Nord Stream 2 pipeline and energy security more broadly, as well as ongoing reforms," the US State Department said in a statement announcing the visit.
While in Kiev, Chollet is scheduled to "meet with senior government officials to discuss U.S. support for Ukraine’s efforts to counter Russia’s aggression and to further advance economic and anti-corruption reforms."
In Warsaw, Chollet plans to "discuss strategic bilateral and regional issues, as well as our shared commitment to democratic values and institutions, with senior government officials and civil society representatives," according to the statement posted on the US State Department's website.
"He will also engage with business leaders to strengthen bilateral economic ties," the statement added.
'Shared concerns about Nord Stream 2'
Last week, US President Joe Biden voiced concern over Russia's Nord Stream 2 gas pipeline project during talks with visiting German Chancellor Angela Merkel.
The Nord Stream 2 project is opposed by Washington, while also being heavily criticised by Poland and other Central and Eastern European countries.
Poland strongly opposes the construction of the pipeline, which is almost complete, amid concerns that it will make the European Union more dependent on Russian gas.
Polish deputies in June passed a motion calling on EU and NATO countries to take action to stop the construction of the pipeline.
The motion warned that the gas link would open the way for Russia to mount an armed attack on Ukraine.
Source: PAP, state.gov