KIEV, Sept. 16 - A decision by rebels in eastern Ukraine to hold elections poses a "great danger" to the peace process, President Petro Poroshenko warned.

He also announced sanctions on over 400 people and 90 legal entities held responsible for Russia's annexation of Crimea and the conflict in the east.

The leader of the self-declared Donetsk People's Republic earlier confirmed the elections would be held on October 18.

The neighboring Luhansk rebel region wants to stage elections on November 1.

The government in Kiev - backed by the EU and the US - says such votes would be in violation of the peace deal signed in Minsk, Belarus, in February.

The agreement envisages that elections in the rebel-held parts can only be held according to Ukrainian law.

The dates of the rebel elections also conflict with Ukraine's plan to hold local polls in the government-controlled regions on 25 October.

For their part, the pro-Russian separatists and Moscow accuse Ukraine of not adhering to the deal.

"I want to stress on the great danger posed by the decision to hold fake elections on 18 October and 1 November," President Poroshenko said on Wednesday.

He also said the rebel move required a "firm" response, signing a decree to apply sanctions for one year against more than 400 individuals and 90 companies.

Mr Poroshenko stressed that the sanctions decision was taken "in co-ordination with our partners from the European Union, the United States of America and other countries.”

The blacklist includes top Russian government officials and separatist leaders in Ukraine's eastern Donbas region.

Almost 8,000 people have been killed since fighting erupted in eastern Ukraine in April 2014, a month after Russia annexed the southern Crimea peninsula.

Ukraine and the West accuse Russia of arming the separatists and also sending its regular troops in eastern Ukraine.

Moscow denies this, but admits that Russian "volunteers" fight alongside the rebels.

The EU and the US have imposed their own sanctions against Russian officials and top allies of President Vladimir Putin. (bbc/ez)