Ukrainian President Petro Poroshenko says there is "no good news" so far at the marathon Minsk peace talks aimed at ending the fighting in eastern Ukraine and that the Russian position at the summit is "unacceptable."

Poroshenko, Russian President Vladimir Putin, German Chancellor Angela Merkel, and French President Francois Hollande have spent some 14 hours discussing ways to resolve deadly fighting in eastern Ukraine.

Poroshenko made his comments during a break in the talks, held at Belarus's presidential palace.

He said there are "conditions that I consider unacceptable," though he declined to give details, and added: "the [negotiation] process is ongoing" and "there is always hope."

Poroshenko said the situation is "difficult" but said that Merkel and Hollande are "helping us a lot."

More than 5,350 people have been killed since April in fighting between Ukrainian forces and Moscow-backed, pro-Russian separatists in eastern Ukraine.