Pro-Russian separatists appear to be making preparations for a fresh offensive in eastern Ukraine, U.S. Defense Secretary Ashton Carter told lawmakers on Wednesday.

The Pentagon chief also said that sanctions imposed by European countries and a decline in oil prices were the most effective way to exert pressure on Russia over its role in the conflict.

Cuban President Raul Castro began a series of meetings with Russian leaders Wednesday during a symbolic visit to Havana's Cold War ally for a World War II victory parade at a time of thawing ties with Washington. 

Castro's presence in Moscow makes him one of a dwindling list of dignitaries and foreign leaders set to attend the grandiose Red Square parade on May 9 to mark 70 years since the WWII victory over Nazi Germany in 1945.

Head of al-Mustaqbal Movement and former Prime Minister Saad Hariri met on Tuesday with French President Francois Hollande in Riyadh.

The meeting comes in light of Hariri's shuttle diplomacy to safeguard Lebanon from the conflict raging in the region.

U.N. Secretary-General Ban Ki-moon will attend celebrations in Moscow on Saturday of the Soviet Union's victory over Nazi Germany in World War II, despite criticism from Ukraine and other central European countries.

Ahead of his visit to Moscow for Victory Day, Ban will travel to Poland to attend commemorations there marking 70 years since the end of World War II and to Ukraine, U.N. spokesman Stephane Dujarric said Monday.

Lithuanian prosecutors said Monday they had detained a Russian citizen suspected of spying, in the latest Cold War-style incident as tensions spiral between the West and Russia.

The suspect is a Russian FSB security service agent who sought to "penetrate governing institutions, law-enforcement and intelligence services," the prosecutor's office said.

Iran is determined to end the "manufactured crisis" over its nuclear program and drafting of a final deal with world powers, though hard, is progressing, Foreign Minister Mohammad Javad Zarif said Monday.

The remarks, on Zarif's official Twitter account, came two days after U.S. Secretary of State John Kerry denounced what he said was "hysteria" from opponents of an agreement, which is due by June 30.

North Korea said Monday its titular head of state would attend a World War II anniversary in Russia this week, after leader Kim Jong-Un cancelled his much-anticipated trip to the Moscow event.

Kim Yong-Nam, the president of the North's rubber-stamp parliament, will participate in the May 9 ceremony to mark the 70th anniversary of the Soviet victory over Nazi Germany, state-run news agency KCNA said.

Western powers are getting set to counter an expertly crafted Russian disinformation campaign over Ukraine which has left them wrong-footed too many times for comfort.

The aim is to win the daily battle for the news headlines, to get the EU and NATO story out to show that Russia's message falls well short of the truth.

Two Ukrainian soldiers and one pro-Russian rebel have been killed over the past 24 hours in fighting in the country's war-torn east despite a shaky ceasefire, officials said on Friday.

A Ukrainian military spokesman said that two soldiers were killed and two wounded as a result of the fighting in which he accused rebels of using heavy arms prohibited by a February truce agreement.

The Ukrainian presidency on Thursday said Russian President Vladimir Putin was open to the deployment of a peacekeeping mission in war-torn eastern Ukraine, after the leaders of both countries spoke by phone with their French and German counterparts.

"In the context of the discussion of ways towards a peaceful resolution (of the conflict), President Putin has accepted the possibility of deploying a peacekeeping contingent to the Donbass region," the presidency said in a statement.