Ukrainian President Petro Poroshenko on Friday has called on all political forces and candidates to unite their efforts for promoting free and fair presidential election in Ukraine this year.

"We must jointly protect the Ukrainian election from hybrid challenges," Poroshenko wrote on Facebook.

He stressed the need to attract international observers to monitor the election campaign, saying it would be an additional guarantee of the transparent electoral process.

On Dec. 31, 2018, Ukraine has officially kicked off the campaign for presidential election slated for March 31 this year.

As of Jan. 3, six potential contenders submitted documents to the Central Election Commission declaring their intention to run for president.

Local experts estimate that several dozens of candidates would participate in the presidential race.