The European Union (EU) renewed sanctions on Monday against the ruling coalition's candidate for presidential elections in Democratic Republic of Congo, Emmanuel Ramazani Shadary, and 13 other senior officials.

The decision is likely to worsen relations between the EU and President Joseph Kabila's government, which has lobbied against sanctions it calls an illegal violation of its sovereignty.

Kabila has also refused to accredit EU election observers despite concerns by opposition politicians, civil society activists and foreign powers about the credibility of the December 23 vote.

He is due to step down next month after 18 years in power and wants Shadary as his successor. Many experts consider him the favourite given the ruling coalition's institutional advantages.

The EU imposed sanctions in 2016 and 2017 on Shadary and 15 other nationals over violent crackdowns on protests and repeated delays to the election, which was originally meant to take place two years ago. Two of the 16 have since been transferred to a UN sanctions list.

Shadary served as interior minister during some of the protests and as a senior official in Kabila's PPRD party.

The sanctions include travel bans and asset freezes, the EU said in a statement, adding it would "review the restrictive measures in the light of and following the elections in the DRC and stands ready to adjust them accordingly".

The vote will mark the country's first democratic transition of power since independence from Belgium in 1960.

Kabila told Reuters on Sunday his government planned to retaliate against the EU.

"There will be (retaliatory) measures, definitely, because we believe those sanctions are politically motivated," he said. "We are not talking about expelling anyone but definitely we will have to pay back in kind one way or the other."

One of the leading opposition presidential candidates, Martin Fayulu, called on Saturday for the sanctions to remain in place.

"The EU should reinforce its sanctions against Shadary to impede the Kabila regime since it's been the cause of many human rights violations," he said at a campaign rally in the city of Kisangani.