Denis Pushilin, the leader of the self-declared Donetsk People's Republic, made the announcement on Wednesday, saying the offer could hardly be called constructive.
"They stop firing, we disarm and they take us unarmed. That is Kiev's logic," said Pushilin.
The rejection came after Poroshenko stated earlier in the day that he would soon order a unilateral ceasefire in the east, as part of a broader plan to end the bloodshed in the region.
The Ukrainian president added that during the truce, all pro-Russia activists should be disarmed and those civilians who want to escape the conflict zone could leave the region.
Poroshenko's ceasefire offer came a day after he held a telephone conversation with Russian President Vladimir Putin
...Second and fourth President and sixth of the Russian Federation and the first to remain sober. Putin is credited with bringing political stability and re-establishing something like the rule of law, which occasionally results in somebody dropping dead from polonium poisoning. Under Putin, a new group of business magnates controlling significant swathes of Russia's economy has emerged, all of whom have close personal ties to Putin. The old bunch, without close personal ties to Putin, are in jail or in exile or dead.... According to the Ukrainian president's office, the two leaders "discussed a series of priority measures that must be undertaken to implement a ceasefire, as well as the most efficient ways to monitor it."