Middle-aged municipal worker Masha bent down in her green parks department overall to tend the pristine flowerbeds on a tree-lined avenue in downtown Donetsk.

"We don't know who will be paying our salaries from now on," she said, digging around in the soil with her trowel.

Among those hit by new sanctions imposed by Brussels on pro-Russian officials are Natalya Poklonskaya, the prosecutor of Crimea who became an Internet sensation for her good looks, and a self-styled mayor of the rebel-held Ukrainian city of Slavyansk.

Vyacheslav Volodin, the hugely influential first deputy chief of Russian President Vladimir Putin's staff, and Vladimir Shamanov, a military commander who gained notoriety for his heavy-handed tactics in volatile Chechnya, were also on a new sanctions list released by the European Union.

Deadly violence flared in the restive east of Ukraine on Tuesday even as Europe stepped up its diplomatic efforts to resolve the escalating crisis on its doorstep.

German Foreign Minister Frank-Walter Steinmeier was in Ukraine to push the Kiev authorities and pro-Moscow rebels to come together at the negotiating table after the East-West security body OSCE drew up a roadmap aimed at easing tensions.

Russian President Vladimir Putin will next week travel to China for a visit expected to see Moscow and Beijing seal a landmark gas agreement, the Kremlin said on Tuesday.

During the May 20 visit to Shanghai, Putin will oversee the signing of a number of "important agreements" in trade and energy, the Kremlin said without providing further details.

German Foreign Minister Frank-Walter Steinmeier said Tuesday that Ukraine's May 25 presidential vote will be crucial in bringing the country out of crisis, after he arrived in Kiev on a key visit.

"We all agree that the presidential election on May 25 will play a crucial role," Steinmeier told reporters after talks with Ukrainian officials, adding that he hoped steps in Ukraine will "bring back occupied territory, disarm armed groups step-by-step and reinstall the authority of the state."

Oil prices were mixed on Tuesday after rallying in the previous session in response to a vote in eastern Ukraine to break away from the country, fuelling fears of a civil war that could disrupt supplies.

The U.S. benchmark, West Texas Intermediate for delivery in June, added 16 cents to $100.75 a barrel, while Brent North Sea crude for June fell three cents to $108.38 a barrel.

The EU was intensifying diplomatic efforts Tuesday to get Ukraine's leadership and pro-Moscow rebels to the negotiating table, as the OSCE said Moscow supports a de-escalation roadmap for the crisis.

German Foreign Minister Frank-Walter Steinmeier kicks things off with an early morning visit to Kiev to support a "national dialogue" between Ukraine and the pro-Russian regions in the east, said his spokesman in Berlin.

Germany this week launches another attempt to mediate in the Ukraine crisis, pushing for dialogue between the pro-Western government and pro-Russian groups to resolve the festering and violent conflict.

Foreign Minister Frank-Walter Steinmeier will visit Ukraine on Tuesday to support a "national dialogue" between Kiev and the pro-Russian regions in the east, said his spokesman in Berlin.

NATO's deputy chief vowed Monday to strengthen the alliance's partnership with Moldova during a visit in the former Soviet country that could inflame tensions with Moscow.

NATO's deputy secretary general Alexander Vershbow wrote on Twitter the alliance is "committed to enhance partnership (with) Moldova in full respect of its neutrality, supporting its independence, integrity and sovereignty."

The United States said Monday it does not recognize the "illegal referendum" held over the weekend in east Ukraine that called for the region to break away from Kiev.

State Department spokeswoman Jen Psaki said the vote organized by pro-Russian elements in Donetsk and Lugansk "was an attempt to create further division and disorder in the country."