A senior aide to Ukrainian President Petro Poroshenko on Thursday accused Facebook of political bias, ahead of a question-and-answer session with co-founder Mark Zuckerberg.

"There is pro-Russian influence and pressure on the Facebook office in Russia," said deputy head of the presidential administration Dmytro Shymkiv, who is negotiating with the global social network to solve the problem.

He claimed Russian moderators are overseeing Ukrainian users and are swayed by the Kremlin's political agenda in the conflict in eastern Ukraine.

Facebook users in Ukraine have flooded the social network with allegations of pro-Russian political bias.

Poroshenko this week made a personal appeal to Zuckerberg to open a separate office in Ukraine to prevent such alleged bias, writing from his own Facebook account.

"We have to use all available channels to get reaction from global companies," Poroshenko said. "Ukraine does need a Ukrainian Facebook office!"

Zuckerberg had invited users to send him questions ahead of one of his question-and-answer sessions to be held later Thursday.

Hundreds of Ukrainians posted comments on Zuckerberg's page backing Poroshenko's call.

Many complained of the banning of users and deletion of posts critical of Moscow's role in the war in eastern Ukraine between pro-Russian separatists and Kiev's forces, which most Ukrainians see as a war with Vladimir Putin's Russia.

Facebook did not respond to requests for comment.

Previously the company has argued that its Russian-language segment is managed from Ireland and does not have a physical office in Russia, although its director is Russian.

Observers in Russia say that Russian Internet "trolls" monitor content critical of the Kremlin and manipulate the Facebook system to instigate a wave of complaints against any user, leading to account blockages.

"In Russia, the battles on social networks are especially acute, and the government uses the services of an online army," said Sergei Parkhomenko, a blogger and journalist.

He recently wrote a post about Russia's alleged involvement in the shooting down of Malaysia Airlines flight MH17 over eastern Ukraine last July.

After the post became popular, Facebook blocked it, Parkhomenko said.

"The topic led to a (troll) attack," he said.

Administrators later apologised and unblocked the post, but the same text, reposted by his wife, was blocked again the next day, he said.

Many Russian "trolls" work out of an office in Russia's northwestern city of  Saint Petersburg and are charged with writing content with a pro-Kremlin slant on blogs and in website comment sections, one former cyber warrior told AFP last month.

"I am sure Facebook is not at fault, they are victims of abuse themselves," Parkhomenko said. "Unfortunately, Facebook is defenceless against this."