U.S. President Barack Obama and Ukrainian President Petro Poroshenko have discussed ways to better control the uneasy border between Russia and eastern Ukraine.
Obama and Poroshenko spoke by phone on October 15.
The White House says they discussed how all sides must live up to a cease-fire deal signed last month in Minsk.
The deal has helped reduce hostilities, but failed to completely halt fighting.
The White House says Obama and Poroshenko also discussed energy security, political reform, and Ukraine's effort to bolster its economy.
Obama praised the Ukrainian parliament's passage of legislation to fight corruption.
The call comes as Russian President Vladimir Putin is due to hold talks with Western leaders about Ukraine.
Putin will take part in a two-day Europe-Asia summit starting on October 16 in Milan.
The gathering offers him the first chance to discuss the Ukrainian crisis with EU leaders since his visit to France in June to attend D-Day anniversary commemorations.
The United States and Europe have sanctioned Moscow over its actions in Ukraine.
The West accuses Russia of sending troops and arms to the pro-Russian rebels in eastern Ukraine, a charge the Kremlin denies.
In an interview with the Serbian daily "Politika," released by the Kremlin on October 15, Putin dismissed Western sanctions as an "absurd and illusory" attempt to isolate Russia.
"It is obviously impossible to achieve it, but the economic health of Europe and the world can be seriously undermined," said Putin, who will make a stopover in Serbia on October 16 before travelling on to Milan.
Putin harshly criticized Obama for mentioning Russia as a major threat to humanity alongside the Ebola virus and the Islamic State group.
"We hope that our partners will realize the futility of attempts to blackmail Russia and remember what consequences discord between major nuclear powers could bring for strategic stability," he said.
Presidential foreign affairs adviser Yuri Ushakov said that Putin will meet on October 16 with German Chancellor Angela Merkel and attend a dinner involving other leaders.
Merkel said she expects to discuss the fulfillment of the cease-fire.
"I expect an open exchange of views and progress in implementing the Minsk agreement. ... We will talk about how we can transform the Minsk agreement into reality," Merkel told reporters in Berlin.
Late last month, Merkel said the EU still wasn't considering removing the sanctions because of ongoing fighting.