Chancellor Angela Merkel's heir apparent faced criticism from across Germany's political spectrum today after she called for rules on expressing online opinions before elections in response to a YouTube video that criticised her party.

Annegret Kramp-Karrenbauer, who replaced Merkel as leader of the ruling Christian Democratic Union (CDU) last year, denied she was promoting censorship.

Her comments came after a popular 26-year-old YouTuber called Rezo called on Germans to boycott the CDU and its sister Social Democratic Party (SDP).

Both parties were hammered in this weekend's European Parliament Elections, with voters, particuarly those under 30, deserting the conservative CDU and SPD coalition.

Merkel appears to have withdrawn support for her successor, claiming she is not up to the top job, and is more determined than ever to stay in office until the end of her term, according to Bloomberg.

Annegret Kramp-Karrenbauer, Chairwoman of Germany's Christian Democratic Union party (CDU) attends a news conference in Berlin yesterday

Government sources claim Merkel has refused to spend any more political capital on supporting AKK after the party suffered its worst election result ever last week.

The new leader has slid in opinion polls in recent months after a series of gaffes that have raised questions about her suitability for the role of Chancellor.

Kramp-Karrenbauer's victory last December in a tight race to succeed Merkel as leader of the CDU put the 56-year-old in pole position to become the next German Chancellor.

Merkel now wants to hold on to her job until her term ends in 2021 and will face an awkward encounter with her rumoured successor when the party meets next week to reflect on their election result.

In March, Kramp-Karrenbauer drew sharp criticism from her Social Democrat coalition partners for poking fun at transgender people in a light-hearted carnival speech.

In February, she was ridiculed for addressing a high-profile meeting of her conservative CDU party by calling them Social Democrats.

In an opinion piece in its online edition on Tuesday, the Sueddeutsche Zeitung wrote: 'Annegret Kramp-Karrenbauer is making so many mistakes that her suitability as chancellor must be in doubt.'

The politician denied she was promoting censorship after her comments, which were prompted by a YouTube video by a popular 26-year-old blogger named Rezo, pictured

In Rezo's video, seen by millions ahead of the vote, the vlogger called on voters to reject the two parties for betraying the young by not addressing the climate crisis.

'I asked myself what would be the response in this country if say 70 newspapers issued a joint appeal two days before the election, saying: 'Don't vote CDU or SPD.'' Kramp-Karrenbauer, widely known by her initials AKK, told reporters on Monday.

'That would have been clear propagandising before the election, and I believe it would have unleashed a lively debate,' she added. 'So the question remains: what are the rules from the analogue era and how do they apply in the digital era?'

She later defended her remarks: 'It is absurd to assume that I want to regulate opinions,' she tweeted.

'But what we have to talk about are the rules that apply during election campaigns.'

Political opponents and allies alike responded with a mix of outrage and surprise. Armin Laschet, a fellow conservative who leads North Rhine-Westfalia, Germany's largest state, quoted the free speech clause of Germany's constitution in a speech.

'Seventy years old but still just right for YouTube. The constitution protects freedom of opinion in all media,' he said, according to a tweet from his staff.

The leader of the pro-business Free Democrats, Christian Lindner, tweeted: 'I can hardly believe it... On the contrary, we need more open debate - on social media too.'

Niema Movassat, a lawmaker with the far-left Linke, tweeted that Kramp-Karrenbauer's comments were 'an attack on freedom of opinion' and added that she 'should resign immediately.'

Germany does not have restrictions on publishing opinions in newspapers ahead of an election, although it does require broadcasters to be politically balanced.