Five export licenses for equipment bound for interior ministry revoked as country braces for another round of mass protests

The British government has revoked five export licences for equipment destined for Egypt in response to reports that security forces have used excessive force in dealing with protests since the fall of ex-president Mohamed Morsi.

The business secretary, Vince Cable, said on Friday the licences concerned the sale of arms components from UK companies to Egypt's military and police forces.

A Foreign Office official told the Guardian the revocation was linked to reports of military and police malpractice during recent protests. A Guardian investigation published on Thursday reported that the deaths of 51 pro-Morsi supporters on Monday 8 July was the result of a co-ordinated assault by both police and army officials on largely unarmed protesters.

The official said the UK government felt there was now an "increased likelihood" that the weapons parts could be used in the excessive repression of protesters in the near future.

"We judge that there is now a clear risk that the equipment covered by these licences might contribute to the excessive use of force during crowd control," said the official, speaking on condition of anonymity.

It is unclear which British companies – and how many of them – have been banned from making the sales. But the official confirmed that the bans concerned the supply of armoured personnel carrier components to Egypt's interior ministry, which controls the police force. They also revoked the delivery to Egypt's military of radios, vehicle aerials, machine-gun components, tracked armoured fighting infantry vehicle components, and tank communication equipment.

The news came as Egypt braced itself for another round of mass demonstrations on Friday with the weeks-long impasse between the Muslim Brotherhood and the country's military-backed interim government – which swept the Brotherhood's Mohamed Morsi from power earlier this month – showing no signs of abating.

Both the Brotherhood and its secular-minded opponents have announced large afternoon protests, with the Brotherhood refusing to leave the streets unless Morsi is restored to the presidency – a demand that will never be agreed to.

For their part, the military and its proxies are equally stubborn – refusing to end a crackdown on the Brotherhood's leadership, with several senior brothers under arrest and their assets frozen. Morsi himself has been imprisoned incommunicado in an unknown location since his removal on 3 July.

There are fears that the impasse could lead to more state killings – such as last week's massacre of Morsi supporters in east Cairo – or a heightening of violence in extremist hotspots such as the Sinai desert.

On Thursday night the new interim president Adly Mansour – a senior judge installed by the army the day after Morsi's departure – issued a veiled warning to the Brotherhood. In a televised speech to the nation, Mansour said the state would not give in to those they see as trying to destabilise the country.

"We are going through a critical stage and some want us to move towards chaos and we want to move towards stability. Some want a bloody path," he said. "We will fight a battle for security until the end."

Almost every state and private media outlet has swung behind the new order, with the government clamping down on those who dare to express alternative narratives. A cameraman for al-Jazeera, the only Arabic-language channel to cover in any detail the sizeable pro-Morsi protests, was arrested as he filmed clashes between Morsi supporters and police earlier this week.

Prosecutors detained al-Jazeera's Mohamed Badr for 15 days after his arrest at the clashes in central Cairo on Monday night. Badr's colleague, producer Mohamed Gomaa, later asked officers what Badr had been detained for. "They said it's enough to accuse him of working with al-Jazeera, because they are traitors, and people working for al-Jazeera want to set the country on fire," Gomaa claimed.

Al-Jazeera is funded by Qatar, also a major financial backer of Mohamed Morsi's administration, and the channel is accused of Brotherhood sympathies. Al-Jazeera's bureau chief was thrown out of an army press conference last week – to applause from other local journalists – while al-Jazeera journalists said they were ejected from another press conference at the presidency on Wednesday.

• This article was amended on 19 July 2013. The original referred to eight export licences being revoked. This has been corrected