U.S. Vice President Joe Biden has spoken with Ukrainian President Petro Poroshenko.
The White House says the two leaders discussed diplomatic efforts to put in place a cease-fire that would hold, be respected by separatists, and supported by Russia.
Biden also threatened further U.S. sanctions against Russia unless it stops supporting separatists and sending arms across the border into Ukraine.
Biden and Poroshenko spoke on July 3 as foreign leaders try to restart peace talks.
U.S. President Barack Obama consulted by phone on July 3 with German Chancellor Angela Merkel and agreed to keep up the pressure on Russia to defuse the crisis in Ukraine or face more economic sanctions.
A unilateral cease-fire declared by Poroshenko expired this week after being violated repeatedly by pro-Russian separatists.
The call comes as Poroshenko is seeking to rejuvenate Ukraine's military and combat corruption by appointing a new defense minister and top general.
New Ukrainian Defense Minister Valeriy Heletey has vowed to hold "a victory parade" in Crimea, which was annexed by Russia in March.
Addressing parliament on July 3, Colonel General Heletey said: "Believe me, there will be a victory parade -- there will be for sure -- in Ukraine's Sevastopol."
Heletey, a former policeman who headed the state's VIP bodyguard service, was approved by lawmakers after being recommended by President Petro Poroshenko.
Corruption In The Army
Lieutenant General Viktor Muzhenko, a career soldier trained in the Soviet Union, was confirmed as the new head of the joint chiefs of staff.
Yury Kosyuk, an agriculture magnate and one of Ukraine's richest men, will oversee defense issues in the presidential administration.
In announcing the appointments, Poroshenko promised to "purge the army of thieves and grafters."
He has pledged to stamp out corruption within the country's armed forces which are battling to assert control over pro-Russian separatists in the country's industrial east.
Meanwhile in eastern Ukraine, government forces pressed their offensive against pro-Russian separatists after the expiration of a 10-day cease-fire late on June 30.
In Berlin, the foreign ministers of Ukraine, Russia, Germany, and France agreed on July 2 to work on another truce, with talks starting July 5 at the latest.
Any future cease-fire would be monitored by the Organization for Security and Cooperation in Europe (OSCE).
The four ministers agreed that the violence should cease on all sides, hostages be released, and Ukraine border points with Russia be brought back under government control.
In a conference call on July 3, French President Francois Hollande and German Chancellor Angela asked Russian President Vladimir Putin to help organize a meeting before July 5 in order to define the conditions for a cease-fire.
In a statement, the Kremlin said Putin expressed his "deep concern" over the growing number of civilian casualties and refugees from eastern Ukraine who are now in Russia.
The Ukrainian Defense Ministry says nearly 200 soldiers have been killed and more than 600 wounded since April, while separatists say at least 800 rebels have been killed.
According to the United Nations, at least 110,000 people have left Ukraine for Russia, and about 54,400 others have been displaced within Ukraine.