Ukrainian tanks and fighter bombers launched a ferocious assault against pro-Russian separatist insurgents on Tuesday after Kiev dismissed European pressure to save a tenuous 10-day truce.

The resumption of the worst fighting in Europe in nearly two decades drew the instant wrath of Russian President Vladimir Putin and set off a new international scramble to regain some control over events in the strategic ex-Soviet state.

Russian President Vladimir Putin on Monday called for Ukraine's truce to be extended and for new talks between Kiev and separatists, just hours before the current ceasefire expires.

"Vladimir Putin stressed the importance of extending a ceasefire as well as creating a reliable mechanism to control the observance of the truce with an active role of the OSCE," the Kremlin said in a statement after Putin held talks with his French counterpart Francois Hollande, Germany's Angela Merkel and Ukrainian President Petro Poroshenko.

All 15 helicopter passengers and crew survived a close brush with death on Monday when their aircraft crash-landed in woods in the Russian Far East, a rare happy ending for a country prone to aviation disasters.

The Mi-8 helicopter, which carried forest firefighters and was conducting aerial reconnaissance, landed near the village of Chekunda in the Khabarovsk region, the Federal Forestry Agency said.

France and Germany on Monday looked set to ramp up pressure on Russia to stem the Ukraine conflict in frantic negotiations as the clock ticks down on a shaky truce.

French President Francois Hollande and German Chancellor Angela Merkel were due to hold four-way telephone talks with Kremlin strongman Vladimir Putin and new Kiev leader Petro Poroshenko ahead of a 1900 GMT deadline for an unsteady ceasefire to end in violence-hit eastern Ukraine.

A journalist with Russian public television has been shot dead in east Ukraine where pro-Moscow separatists are battling Ukrainian forces, the media worker's employer Channel One said Monday.

Anatoly Klyan, a 68-year-old cameraman, was among a group of Russian journalists on a reporting trip with the insurgents, the TV channel said.

French President Francois Hollande and German Chancellor Angela Merkel spoke for "over two hours" with their Russian and Ukrainian counterparts Sunday, the Elysee said, with the latest ceasefire deadline in Ukraine looming.

During the telephone exchange with Russia's Vladimir Putin and Ukraine's leader Petro Poroshenko, the leaders discussed "the importance of making new concrete advances in the security situation on the ground, prolonging the ceasefire and putting in place the peace plan" presented by Ukraine, the French president said in a statement.

More than 1,200 Chinese workers have been relocated from conflict-torn northern Iraq to Baghdad, state media said on Sunday, as Iraqi troops fight back against a militant onslaught.

The employees of the state-run China Machinery Engineering Corp (CMEC) were successfully evacuated late last week and are due to return to Beijing, the official Xinhua news agency reported.

Iraqi forces pressed a counter-attack on Saddam Hussein's hometown of Tikrit Sunday as Russia delivered Sukhoi warplanes to aid Baghdad in what diplomats warn is an existential battle against Sunni militants.

Alarmed world leaders have urged a speeding up of government formation following April elections, warning the conflict driven by sectarian divides cannot be resolved militarily.

Russia said Saturday that three shells fired by Ukrainian troops have hit a customs post and residential areas inside its territory, causing damage but no injuries.

"In the course of clashes on Ukrainian territory, the Ukrainian military fired shells which ended up on Russian territory," a spokesman for the border service in the Rostov region, Vasily Malayev, told Russian agencies.

Russian Deputy Foreign Minister Sergei Ryabkov said in Damascus on Saturday that his country "will not remain passive" as jihadists push an offensive in Syria's neighbor Iraq.

"Russia will not remain passive to the attempts by some groups to spread terrorism in the region," Ryabkov told journalists after meeting with President Bashar Assad.