Ukrainian President Petro Poroshenko said on Tuesday government forces would renew offensive operations against rebels and "free our lands", hours after a ceasefire to allow for peace talks with the pro-Russian separatists had expired.
Poroshenko, who accuses Russia of fanning violence in eastern Ukraine, dismissed Moscow's offers to defuse the crisis, and accused the rebels of failing to keep to the truce or follow a peace plan he had outlined. "We will attack and free our lands. The decision not to continue the ceasefire is our answer to terrorists, militants and marauders," he said in a televised statement delivered in front of the blue-and-yellow Ukrainian flag.
In a statement on his Facebook page, the 48-year-old leader said: "Taking into account all the circumstances, I can affirm that things will be difficult, but we must be united, because we are fighting to free our land from dirt and parasites."
The announcement came after a four-way phone call with Russian President Vladimir Putin and German and French leaders aimed at helping end the crisis in the Russian-speaking east where government forces have been battling rebels since April.
In eastern Ukraine's flashpoint city of Slaviansk, a rebel stronghold since separatists took over the city in April, shelling could be heard, though it was unclear from which direction it was coming from.
Poroshenko said he was willing to return to a ceasefire "at any moment" if it became clear that all sides were ready to carry out all aspects of the peace plan, including the freeing of hostages and creating effective border controls.
The president, who had been under Western pressure to extend the ceasefire, is facing rising anger at home over the military deaths. Local media said hundreds of people had gathered outside of his administration building in Kiev in anticipation of a statement on the fate of the truce.
There was no immediate response from the Kremlin. But the speaker of Russia's lower house of parliament called for a new ceasefire, Interfax news agency reported.
"We think that without a truce, without the start of dialogue, it is simply impossible to restore peace, justice and law and order in Ukraine," Sergei Naryshkin, an ally of Putin, was quoted as saying.
Poroshenko had extended a government ceasefire last week until 10 p.m. (1900 GMT) on Monday to allow for peace talks with a contact group involving separatist leaders, a former Ukrainian president, a senior representative of the OSCE rights and security body and Moscow's ambassador to Kiev.
"The unique chance to implement the peace plan was not realised. It happened because of the criminal actions of the militants. They publicly declared their unwillingness to support the peace plan as a whole and in particular the ceasefire," Poroshenko said.
Pro-Russian separatism erupted in Ukraine's east in April after street protests in Kiev toppled a Moscow-backed president, Viktor Yanukovich, after he had walked away from a free trade deal with the European Union that would shift Ukraine westwards.
Russia subsequently annexed Crimea and separatist rebels in Ukraine's Russian-speaking east seized buildings and strategic points, declaring "people's republics" and saying they wanted union with Russia.
Poroshenko last Friday signed the EU deal which Yanukovich balked at in defiance of threats by Russia to carry out retaliatory trade action.
Moscow could face more penalties from the EU on top of existing asset freezes and visa bans unless pro-Russian rebels act to wind down the crisis in the Ukraine's Donetsk and Luhansk provinces.
A statement tweeted by the Foreign Ministry said 27 Ukrainian servicemen had been killed and 69 wounded since the ceasefire began on June 20.
At Putin's request, the Russian parliament last week revoked the right it had granted him in March to invade Ukraine in defence of its Russian-speakers.
Russian Foreign Minister Sergei Lavrov told state TV Moscow was ready to allow OSCE security and rights watchdog monitors and Ukraine's border guards to enter the Russian side of the border for joint control. Kiev accuses Russia of letting fighters and arms to cross the border into eastern Ukraine.
"The revocation of permission (by lawmakers) to send Russian troops into Ukraine was positive but symbolic," Poroshenko said.
EU leaders said on Friday they were ready to meet again at any time to adopt more sanctions on Russia. Diplomats said they could target new people and companies with asset freezes as early as next week. More than 60 names are already on the list.
Although it has drawn up a list of hard-hitting economic sanctions, the EU is still hesitating over deploying them because of fears among some member states of antagonising Russia, their major energy supplier.