Hungarian Prime Minister Viktor Orban has apologised to European conservative parties for calling them "useful idiots" over an anti-EU billboard campaign that could see his party ejected from the European Parliament's dominant centre-right EPP bloc.

In a newspaper interview earlier this month, Orban called critics within the EPP "useful idiots" and accused them of helping the group's leftwing and liberal opponents ahead of European Parliament elections in May.

"I would hereby like to express my apologies, if you found my quote personally offensive," Orban said in his letter to the Belgian Christian Democratic & Flemish (CD&V) party which was published by newspaper.

The letters were sent Wednesday to leaders of 13 member parties of the EPP who have proposed expelling Orban's ruling Fidesz party from the bloc, Orban's press chief Bertalan Havasi told Hungarian newswire MTI.

In the letter, Orban asked party leaders to "reconsider your proposal for expulsion".

While Fidesz "do not wish to change our own position... on the issue of migration, the protection of Christian culture and the future of Europe", disagreements should not be solved by expelling a party "from our political family", he said.

The controversial billboard campaign accuses European Commission President Jean-Claude Juncker and liberal US billionaire George Soros, a bete-noir of Orban's, of plotting to flood Europe with migrants.

Similar messages have appeared on television and internet websites while Orban has also sent letters to households nationwide that attack Juncker.

Juncker did not receive a letter of apology from Orban, according to European Commission spokeswoman Margaritis Schinas. He said Juncker stood firm in his position that EPP members must respect the group's "basic values".

A decision on the future membership of Fidesz will be on the agenda at an EPP meeting on March 20, according to Manfred Weber, the bloc's leading candidate to replace Juncker later in the year.

Weber met Orban in Budapest on Tuesday and called for the populist leader to apologise for the campaign.

"We had talks in a constructive atmosphere but problems are not yet solved," Weber told reporters.

Weber has demanded that Orban meet three conditions for Fidesz to remain in the EPP, including withdrawing the anti-EU campaign, and apologising to EPP member parties.

The anti-Juncker campaign had "created a burden and damage to the EPP," Weber said last week.

Weber also wants Orban to let the CEU university founded by Soros stay in Budapest.

The government said it would stop the anti-EU campaign by Friday but the messages were still visible Thursday in newspapers and on internet sites.

(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)