"We've got observers from the OSCE, some of whom have been denied access by pro-Russian groups and I suggested to him that one way we could contribute to some kind of stable outcome would be if he on his side and me on my side could seek to get those observers in there so that we could have a neutral party tell us what's going on," Dempsey told The Associated Press, following a military symposium in Dallas, Texas.
Former Ukrainian Prime Minister Yulia Tymoshenko told The Associated Press in an interview on Saturday that she welcomed further sanctions against Russia and called for NATO membership for Ukraine to protect itself from Russian aggression.
Tymoshenko, who is running in the May 25 presidential election, said that while only a minority of Ukrainians supported NATO membership previously, Russia's aggressive actions in the country's east had forced a "fundamental change" in public thinking.
Her tough talk underscores the increasingly tense relationship between Russia and Ukraine in recent weeks — acting prime minister Arseniy Yatsenyuk warned Friday that Russia "is keen to start World War III."
On Saturday, Yatsenyuk traveled to Rome to meet with Pope Francis and Italian Premier Matteo Renzi. Francis gave Yatsenyuk a fountain pen, telling him, "I hope that you write 'peace' with this pen."
Yatsenyuk replied: "I hope so, too."
In a briefing with reporters, he lashed out at Moscow, saying Russian military aircraft violated Ukrainian air space late on Friday.
"The only reason is to provoke Ukraine to strike a missile and to accuse Ukraine of waging a war to Russia," he said, and asked Russia "not to provoke and not to support Russian-led terrorists... in eastern and southern Ukraine. We ask Russia to leave us alone."
The Russian Defense Ministry denied claims, first raised by the U.S. on Friday, that its aircraft had crossed the border with Ukraine, a spokesman told state news agencies on Saturday.
The streets of Slovyansk were relatively calm Saturday. Hundreds of mourners, including Ponomarev, went to a local church to pay respects to a pro-Russian insurgent apparently killed during a clash with Ukrainian government troops earlier in the week.
Ukraine's acting president this week ordered security forces to resume operations in the country's east after the bodies of two people allegedly abducted by pro-Russia insurgents were found and a military aircraft was reported to have been hit by gunfire.
That came despite an international agreement calling for all sides in Ukraine to refrain from violence and for demonstrators to vacate public buildings. It didn't specifically prohibit security operations, but Ukraine suspended an earlier so-called "anti-terrorist operation" after the accord.
Associated Press writers Laura Mills in Moscow, John-Thor Dahlburg in Brussels, Frances D'Emilio in Vatican City, Pietro De Cristofaro in Rome, Frank Jordans in Berlin, Nedra Pickler in Washington and Emily Schmall in Dallas, Texas contributed to this report.
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