BRUSSELS (AFP) ― New European Commission chief Jean-Claude Juncker stoked a bitter row between London and Brussels Wednesday, accusing Prime Minister David Cameron of having a “problem” with other EU leaders.

Juncker opened his first press conference as head of the EU’s powerful executive arm with an attack on “unjustified criticisms” by both Cameron and Italian Prime Minister Matteo Renzi at a summit in October.

But he reserved his harshest words for Cameron, who is fighting Brussels over a budget backpayment demand for 2.1 billion euros ($2.6 billion) against the backdrop of a possible referendum on Britain’s EU membership in 2017.

“I am not the type who trembles, in front of prime ministers or at any other time,” said former Luxembourg Prime Minister Juncker.

“I don’t have a particular problem with Mr. Renzi, whom I have great respect for.

“I don’t have a problem with Mr. Cameron, Mr. Cameron has a problem with the other prime ministers.”

Juncker is known for his blunt way with words but his remarks still raised eyebrows in Brussels where his predecessor Jose Manuel Barroso was more guarded, stressing the importance of keeping Britain in the EU.

But in recent months, there have been signs of a growing impatience with Cameron, a feeling that enough may be enough given that his EU-bashing seems driven by domestic political concerns.

Cameron had strongly opposed Juncker’s appointment earlier this year, seeing him as an insider and federalist who would not adopt the EU reforms Britain demands before the referendum, and the budget row has deepened the rift.

But the stridently euroskeptic U.K. Independence Party is set to steal another parliamentary seat from Cameron’s Conservative Party later this month, putting the prime minister under huge pressure from restive supporters attracted by UKIP’s antiimmigration stance.

Meanwhile reports this week said German Chancellor Angela Merkel had warned Cameron he was approaching a “point of no return” with his own proposals for immigration controls.

The British leader’s spokesman rejected Juncker’s criticisms.

“Does the prime minister always put the interests of British citizens and British taxpayers first? Of course. He is going to keep doing that. But he works very closely with his EU counterparts,” the spokesman said.

Juncker’s comments came a day after he told the European Parliament that Cameron and Renzi had misled their citizens by saying one thing during the October summit and another to the media afterwards.

Cameron had said he confronted other leaders at the summit, bluntly refusing to pay the budget bill.

Separately, Renzi had vowed at the summit to make public the cost of European Union “palaces” in a row over Italy’s own budget projections.

On Tuesday, Renzi hit back, demanding “respect” from Juncker.

“I’m not going to Europe to say ’please listen to us’, I’m not going with my hat in hand.”