Kiev: Ukrainian President Petro Poroshenko said on Wednesday that the situation in the war-torn east had changed dramatically since a truce was signed last week.
But he again vowed that the separatist eastern regions, where the rebels have declared their own republics, would remain part of Ukraine, saying there was a "war for the independence and integrity" of the country.
"Ukraine will not make any concessions on issues of its territorial integrity," he told a cabinet meeting.
However, a rebel leader insisted that the separatists still intended to break away from Kiev`s rule.
"We are not considering remaining part of Ukraine," Andrei Purgin, the deputy prime minister of the self-proclaimed Donetsk People`s Republic, told AFP in Moscow.
Poroshenko acknowledged that implementing the ceasefire signed in the Belarussian capital Minsk on Friday had been "difficult", with what he described as repeated attempts by rebels to provoke Ukrainian troops to fire.
But he added: "The situation has radically changed at the front.
"Before the ceasefire was announced, Ukraine was losing the lives of dozens of its heroes on a daily basis."
More than 2,700 people have been killed in five months of fighting since pro-Russian separatists launched an uprising in the east in April, and at least half a million have fled their homes.
Poroshenko also said he would submit to parliament a bill granting parts of the mostly Russian-speaking regions more autonomy but keeping them part of the ex-Soviet state.
"There is and can be no talk of federalisation or some estrangement (by the rebel-held regions)," he told the meeting.
"The law on temporary self-rule in individual districts of the Donetsk and Lugansk regions provides for a status that keeps these regions in Ukraine."