Jeremy Corbyn has accused David Cameron of showing "contempt" for democracy and human rights by "rolling out the red carpet" for Egyptian president Abdel Fatah al-Sisi.
Branding Mr Sisi a "coup leader", Mr Corbyn said inviting him to Britain made "a mockery of government claims to be promoting peace and justice in the region".
The Labour leader's intervention came ahead of Mr Sisi's arrival for talks with the Prime Minister.
Earlier this week Labour QC Baroness Kennedy of the Shaws told the House of Lords Mr Sisi had been "responsible for the murder of at least a thousand unarmed protesters" and urged Mr Cameron to confront him over "his tyranny".
But Lord Courtown defended the decision to invite the president, saying Egypt was "key" to the UK's national interest in countering extremism and combating Islamic State (IS)
"It is in Britain's interest to work with President Sisi. Together we need to combat terrorism, we need to counter extremism and help bring stability to Libya," he said.
Downing Street has previously insisted that "no issues are off the table" during bilateral discussions with the former head of Egypt's armed forces, who overthrew Islamist president Mohammed Morsi.
Mr Corbyn said: "David Cameron's invitation to Britain of the Egyptian president and coup leader Abdel Fatah al-Sisi shows contempt for human and democratic rights and threatens, rather than protects, Britain's national security.
"Support for dialogue and negotiated conflict resolution in the Middle East is vital to us all. But to welcome and bolster with military support the coup leader who overthrew a democratically elected president in 2013 and has presided over the killing and jailing of many thousands since makes a mockery of Government claims to be promoting peace and justice in the region.
"Support for dictatorial regimes in the Middle East has been a key factor fuelling the spread of terrorism. Rather than rolling out the red carpet to President Sisi, the Prime Minister should suspend arms exports to Egypt until democratic and civil rights are restored."
Mr Sisi is set to discuss the situation in Libya with Mr Cameron, after warning that the country had been left "without leadership" in the wake of the Nato-led campaign to remove Muammar Gaddafi in 2011.
He told the Daily Telegraph: "Libya is a danger that threatens all of us. If there is no government then this only creates a vacuum where extremists can prosper."
Of the Nato campaign, he added: "It was a mission that was not completely accomplished. What happened was that Libya was left without leadership when it needed our help most.
"Now we have a situation where the will of the Libyan people is being held hostage by militant groups."
Mr Cameron spoke with Mr Sisi by telephone last night to offer his condolences for the Russian plane crash over Sinai.
"They agreed it was important not to pre-judge the investigation, but noted that there was still uncertainty about the cause of the crash and agreed it would be prudent to ensure the tightest possible security arrangements at Sharm el-Sheikh airport as a precautionary measure," a No 10 spokesman said.
A source close to Mr Corbyn confirmed that the Labour leader will not meet Mr Sisi during his visit.
Asked how Mr Corbyn squared his opposition to Mr Sisi's invitation with his own previous talks with Hamas and Hezbollah, the source said: "Jeremy's record is that he has worked to find peaceful and political solutions to conflicts. He supports dialogue, he doesn't support military overthrow of democracies."
Andrew Smith, of Campaign Against Arms Trade, said the UK Government had suspended 49 military licences following the overthrow of Mohamed Morsi's democratically elected government in 2013, only for 24 of the suspensions to be lifted a year later.
The coalition government presided over a total of £156 million worth of arms sales to Egypt, including £85 million since Morsi's ousting, said CAAT.
Mr Smith said: "The uprisings of 2011 were fuelled by a desire for human rights and democracy - a desire that has not gone away, but that is being suppressed by a cruel, authoritarian regime.
"If the Government cares about human rights and democracy then it must end arms sales to Egypt and put a stop to the political support that bolsters the regime."