Nick Clegg has launched an attack on Conservative plans to limit the power of the European Court of Human Rights.
He accused David Cameron of lining up "with Vladimir Putin and other tyrants around the world by tearing up our long tradition of human rights".
Tory "extremists" - or "head bangers" - had won out over moderates like Ken Clarke and Dominic Grieve, sacked in this week's reshuffle, he claimed.
Ex-Attorney General Mr Grieve is said to have warned against the change.
BBC Political Editor Nick Robinson said Downing Street had rejected any suggestion that the purpose of Mr Cameron's reshuffle was "to clear the decks for an assault on the European Court of Human Rights and says no final decision has been taken on what will be in the Conservative manifesto".
Under the Conservative proposals, the UK Parliament will decide what constitutes a breach of human rights.
BBC political editor Nick Robinson said a report written by a working group of Conservative lawyers predicts the so-called British Bill of Rights could force changes in the way the Strasbourg court operates.
By Nick Robinson, BBC Political Editor
Who will rid me of this troublesome court?
That's the question David Cameron badly wants an answer to before the next election.
But it also acknowledges that it could lead to the UK being expelled from the 47-member Council of Europe, which aims to uphold human rights across the continent.
Mr Grieve had warned his colleagues that the idea was a plan for "a legal car crash with a built-in time delay", Nick Robinson said.
The former Attorney General argued that it was an "incoherent" policy to remain a signatory to the European Convention of Human Rights but to refuse to recognise the rulings of the court which enforces it.
Speaking on his weekly LBC radio phone-in, Nick Clegg said he had been "blindsided" by the announcement, which he said revealed the true motive behind Mr Cameron's cabinet reshuffle.
"It's nothing to do with gender balance. It's all to do with the death knell of the reasonable internationalism of people like Ken Clarke," said the deputy prime minister.
"I think the head bangers have now won. They are now saying, in effect, that the Conservative Party are turning their back on a long British tradition of upholding human rights across the world.
"What on earth are we going to say to the dictators in Belarus, to Vladimir Putin, if we do as the Conservatives now appear to recommend, which is to basically say we are going to stamp our little feet and not abide by binding, international human rights practices and conventions?"
'Sense of direction'
The battle to deport radical cleric Abu Qatada and attempts to remove foreign criminals have led to clashes between ministers and the Strasbourg-based court.
In 2012, Mr Cameron warned that the concept of human rights was being "distorted" and "discredited" by controversial decisions in Europe.
Nick Robinson said Downing Street had said no final decision had been taken, but he understood it was planned as a centre-piece of David Cameron's Conservative Party conference speech this autumn.
The Conservatives cannot act in this Parliament because their Liberal Democrat coalition partners are strongly committed to the convention.
Conservative Justice Secretary Chris Grayling told BBC Radio 4's The World at One on Wednesday: "We will produce our full package in due course but ahead of the election and in time for our election manifesto.
"We will curtail the role of the European Convention on Human Rights in the UK. We will replace Labour's Human Rights Act (enshrining the convention in British law).
"We will have a balance of rights and responsibilities in our law , which I think is very important, and we will have a Supreme Court that is supreme. That gives a very clear sense of direction, of the big change which is what I think we need."
Labour's shadow justice secretary Sadiq Khan called on the government to publish Dominic Grieve's advice on the role of the European Court of Human Rights.
"It is now clear that David Cameron sacked Dominic Grieve as he didn't like the advice he was receiving from an experienced lawyer who knew that the Tory's half-baked plans would leave our international standing in tatters," he said.