In flashpoint cities of eastern Ukraine, uneasy residents voiced doubt Saturday that the ceasefire deal would bring lasting peace after five months of devastating conflict that has ruined the lives of so many.

"Nothing has actually changed," 38-year-old Vladyslav Lobsin told Agence France-Presse in the strategic port city of Mariupol, where residents had been bracing for a rebel onslaught until the guns were ordered silent.

Ukraine said Saturday a truce was largely holding in the war-battered east, despite fears it may ultimately fail to halt a pro-Russian insurgency still threatening to tear the country apart.

The 12-point pact signed on Friday is the first backed by both Kiev and Moscow to end a conflict which triggered the most serious crisis between Russia and the West since the Cold War.

Russia on Saturday sent six ships carrying personnel and equipment to a Soviet-era military base in the Arctic that it is reopening to bolster its presence in the region, Russian news agencies reported.

Moscow is ramping up its military presence in the pristine but energy-rich region as other countries such as Canada and Norway are also staking claims to access its resources.

Russian Ambassador to Lebanon Alexander Zasypkin warned of the threat of Islamist extremists on Lebanon given its spread in Iraq and Syria, reported As Safir newspaper on Saturday.

He told the daily: “Lebanon has turned into a front to confront the Islamic State group, but it is not directly connected to the situation in Iraq and Syria.”

Washington's new Moscow envoy John Tefft swiftly took to Twitter upon arrival in Russia, saying on Friday that he was looking forward to what promises to be a tricky job.

"I am very happy to be back in Russia," Tefft, known for supporting the pro-Western aspirations of former Soviet states, said on the U.S. embassy's Twitter account in Russian. 

As the thunder of heavy combat echoed nearby, 25-year-old Yelena said she and her friends were ready to up sticks and flee the Ukrainian port of Mariupol, fearful of a major rebel assault on the city despite hopes of a truce.

"We don't believe (there will be a ceasefire) but we can hope," she told AFP on the eastern edge of the flashpoint city where fresh fighting erupted shortly before talks on the proposed truce open in Belarus.

Ukraine's Russian-backed separatists said they had agreed with Ukrainian officials on a ceasefire starting Friday, at peace talks in Minsk.

"Representatives of Ukraine and Donetsk People's Republic and Lugansk People's Republic signed a ceasefire protocol from 6 pm on Friday," the Twitter account of the so-called Donetsk People's Republic said, without providing further details.

The United States is preparing fresh sanctions against Russia over the Ukraine crisis in coordination with Brussels, which plans to announce further punitive measures on Friday, a White House official said.

"We work on this in coordination with the Europeans," Deputy National Security Adviser Ben Rhodes said on Thursday, adding: "If Russia escalates (in Ukraine), we are prepared to escalate our pressure."

Former U.S. presidential contender and outspoken Kremlin critic John McCain warned on Thursday that Western allies risked leaving behind a "landlocked Ukraine" unless they provided Kiev with weapons to fend off Russia.

The Republican senator alleged that Russian President Vladimir Putin had pushed 4,000 troops and a vast quantity of tanks across the border to help separatist fighters in Ukraine establish a land-link with the Crimea peninsula which Moscow seized from Kiev in March.

Ukrainian President Petro Poroshenko announced that a ceasefire plan aimed at halting five months of conflict in the industrial east would be signed on Friday.

His comments, on the sidelines of a NATO summit largely devoted to the crisis in Ukraine, followed talks on a peace blueprint between Poroshenko and Russian President Vladimir Putin on Wednesday.