Weber threatens to expel Hungary's Fidesz from EPP

The Hungarian leader should also apologise for insulting fellow EPP members, Weber, who is in the race to be the next European Commission president, added.

"My main message is that during the last few weeks Viktor Orban and the Fidesz party again crossed red lines," Weber told journalists at a campaign event in Passau, in the German region of Bavaria, the same day.

"I must tell you all options are on the table ... the ball is in Budapest's court," Weber added.

He gave Orban an ultimatum to fall into line by 20 March, when the EPP's political assembly was to discuss his potential defenestration.

"The next two weeks will be crucial. All options are on the table, especially expulsion," Weber said on Tuesday.

Weber's letter to Daul went into more detail on Orban's sins.

"The repeated attacks on EPP leaders, the unwillingness to resolve open infringement procedures, and in recent days, the attacks against other EPP member parties ('useful idiots') severely damage the unity of our party," Weber wrote.

If Fidesz fulfilled his conditions, it "would send a signal that it continues to be interested in being a member of the EPP", Weber said.

But if Orban failed to blink, "the only option would be to exclude the party from the EPP", Weber added.

Hungary expelled the CEU, which is founded by US philanthropist George Soros, last September, forcing the international school to relocate to Vienna.

Orban more recently caused outrage by putting up posters saying that the current EU commission president, Jean-Claude Juncker, a fellow EPP man, was part of a conspiracy with Soros to flood Hungary with asylum-seekers.

He also called his EPP critics "useful idiots" who were weakening the group in a newspaper interview last Sunday.

Weber's warning came after at least 12 national parties from the EPP, the largest bloc in the European Parliament, also sent letters to Daul calling for Fidesz' expulsion.

The EPP political assembly will discuss the issue at a meeting in Brussels on 20 March.

Orban's latest antics come in the context of long-simmering frustration in the EPP over his illiberal style of rule and nationalist rhetoric.

A majority of MEPs, including most EPP deputies and Weber personally, voted to open an EU sanctions procedure against Hungary on abuse of rule of law last year.

Weber's Christian Social Union (CSU) party from Bavaria has traditionally had close ties with Fidesz, but annoyance over Orban's trolling of the EPP has reached new heights in Munich, the Bavarian capital, and Berlin.

For her part, Annegret Kramp-Karrenbauer, the head of the CSU's sister party, the Christian Democratic Union, who is tipped to be Germany's next chancellor, will meet Orban in Brussels on 19 March.

The Hungarian leader has said his government would stop the Juncker-Soros billboard campaign on 15 March.

But it is unlikely Orban will bow to Weber's demands.