* Ukraine president has threatened not to extend ceasefire
* Putin says tens of thousands forced to flee violence
* Ukraine signs trade and political pact with EU (Adds details, background)
By Maria Tsvetkova
MOSCOW, June 27 (Reuters) - Russian President Vladimir Putin said on Friday a long-term ceasefire was needed in Ukraine to allow talks between the Kiev government and representatives of eastern regions where rebels are waging an armed insurgency.
Putin spoke several hours before a ceasefire announced by Ukrainian President Petro Poroshenko was due to expire and his remarks appeared intended to increase pressure on him to extend it.
"Most important is the securing of a long-term ceasefire as a necessary condition for substantive talks between the authorities in Kiev and representatives of the southeastern regions," Putin said at a diplomatic ceremony in the Kremlin.
"We sincerely strive to help the peace process," he said.
Kiev, which blames its former Soviet master Moscow for fanning the violence, has warned that the ceasefire due to expire at 10 p.m. (1900 GMT) may not be extended without meaningful developments in peace talks.
Poroshenko, under Western pressure to extend the ceasefire, has voiced fears that the truce could be used by separatists in east Ukraine to regroup and re-arm.
Numerous breaches of the ceasefire - including the downing of a helicopter by rebels in which nine servicemen were killed on Tuesday - have increased domestic pressure on Poroshenko to scrap the ceasefire.
In the French city of Strasbourg on Thursday, Poroshenko said almost 150 Ukrainian servicemen had been killed by rebels, including 18 in the past week since the ceasefire was declared.
Putin also said the violence in eastern Ukraine, following the ouster of Moscow-backed former president Viktor Yanukovich had forced tens of thousands of Ukrainians to seek refuge abroad, including in Russia.
Putin has described Yanukovich's overthrow, and replacement by pro-Western leaders, as an "unconstitutional revolution".
Russian officials have warned Kiev of "grave consequences" and economic measures if an economic integration pact signed with the European Union on Friday hurts Russia's economy, which is deeply integrated with Ukraine's.
German Chancellor Angela Merkel spoke to Putin twice this week in telephone calls which a Berlin government source said was aimed at finding a way of prolonging the ceasefire.
Poroshenko, installed as president on June 7 and under pressure from his electorate not to bow to the separatists, has said government forces would switch to a "detailed Plan B" - widely assumed to be a government offensive if the rebels use the ceasefire to buy time.
Western governments, which have introduced several rounds of economic sanctions on Russia for its role in the Ukraine crisis, including the annexation of Ukraine's Crimea territory, have piled pressure on Putin to take steps to disarm the rebels. (Reporting by Maria Tsvetkova; Writing by Thomas Grove; Editing by Timothy Heritage)