The European Union on Friday slapped a travel ban and asset freeze on 11 people allegedly linked to separatist violence in eastern Ukraine.

The decision brings the total number of people on an EU sanctions blacklist to 72, with two firms in Crimea also subject to an asset freeze, an EU statement said.

Ukraine has vowed to make pro-Russian rebels pay after losing 23 servicemen in clashes across the separatist east, while Russia proposed a U.N. resolution demanding a ceasefire to Europe's deadliest conflict in decades.

The Ukrainian defense ministry said Friday the death toll included 19 troops killed in a hail of rockets fired from a truck-mounted Grad rocket launcher system -- a type of weapon both Kiev and Washington insist could only have been covertly supplied to the rebels by Russia.

Russian President Vladimir Putin said Thursday he hopes to increase Russian investments in and trade with Latin America.

During a tour in Cuba that will also take him to Argentina and Brazil, the Russian leader said he was focusing on enhancing technological cooperation and investment, especially in the sectors of energy, nuclear power and machinery.

Moscow said on Thursday there were signs of progress at talks between world powers and Tehran on Iran's nuclear program and that it expected to reach a compromise before a deadline later this month.

"The discussions are quite difficult, but there are clear signs of progress," foreign ministry spokesman Alexander Lukashevich said of the negotiations under way in Vienna.

Russian President Vladimir Putin looks set to meet German Chancellor Angela Merkel amid tensions over Ukraine when both leaders attend the World Cup final in Rio de Janeiro, the Kremlin said Thursday.

Presidential adviser Yury Ushakov said the meeting had not been finalized but Putin was due to have a series of bilateral encounters with world leaders at the match on Sunday and that a tete-a-tete with Merkel appeared to be on the cards. 

Ukraine warned on Thursday that its assault on pro-Russian insurgents may last another month and rejected calls for a ceasefire as it moved tanks within striking distance of the rebels' two remaining strongholds.

An AFP team about 20 kilometers (12 miles) south of the eastern hub of Donetsk -- to which most of the militias have retreated -- saw heavy armored vehicles fan out across the rolling corn and sunflower fields of the economically-vital rustbelt.

Russia's popularity around the world is sagging, and so too is confidence in the way President Vladimir Putin handles global affairs, a 44-nation survey published Wednesday suggests.

In the wake of the Ukraine crisis, 74 percent of Europeans, 72 percent of Americans and 68 percent of Middle East respondents said they have unfavorable views of Russia, according to the Pew Research Center poll.

The United States is prepared to impose tough new economic sanctions on Russia "very soon" if Moscow refuses to sever ties with Kremlin-backed separatists in eastern Ukraine, a U.S. official told lawmakers Wednesday.

But senators, frustrated with U.S. inaction, said Washington's repeated threats ring hollow.

Russia said Wednesday it had arrested a Ukrainian helicopter navigator and charged her over the deaths of two Russian journalists in an attack in eastern Ukraine last month, prompting a furious reaction from Kiev.

Russian investigators said Nadiya Savchenko, one of the few women serving in the Ukrainian airforce, was an accomplice in what they claimed was the deliberate murder of the journalists.

Rebel strongholds in eastern Ukraine braced for more fighting on Wednesday as European leaders prepared to pile new pressure on President Petro Poroshenko for a truce with pro-Russian separatists.

French President Francois Hollande and German Chancellor Angela Merkel were expected to push the Western-backed leader on a ceasefire in three-way telephone talks but Kiev has until now shrugged off calls to halt an offensive that has reclaimed a string of key rebel towns.