Three of the figureheads of Egypt's 2011 uprising have been jailed for three years, the first secular activists to be sentenced in a crackdown that has previously centred on Islamist supporters of the former president Mohamed Morsi.

Ahmed Maher, Ahmed Douma and Mohamed Adel – all senior members of the 6 April youth movement that stirred dissent during the final years of the Mubarak era – were also fined for flouting a new law that rights groups argue severely curtails the right to protest. They were accused of organising an unsanctioned street protest deemed illegitimate by a controversial new law, and of assaulting a police officer.

All three men were also targeted under Morsi's presidency, and campaigned for his removal in July. Their custodial sentence on Sunday is proof that the current administration is seeking to stamp out secular as well as Islamist opposition, say fellow campaigners.

"The repression happening now to the movement and to other NGOs [non-governmental organisations] is even higher than what we experienced in [Hosni] Mubarak's time," said Amr Ali – Maher's successor as leader of 6 April – in the build-up tojust before the verdict. "Mubarak's regime is trying to get power back, and there is a systematic approach of revenge against groups and movements that stood against it.

"Whoever's ruling now is more or less depending on a policy of fear – under the name of fighting terrorism and fighting the Islamists."

Dozens of other secular activists await sentences for similar charges, including Alaa Abd El Fattah, another figurehead of the 2011 uprising. The Egyptian Centre for Economic and Social Rights (ECESR) – a prominent NGO run by a former presidential candidate – was the subject of a violent raid on Thursday, after the group angered the security establishment in recent months by giving legal support to striking workers and jailed Syrian refugees.

For many campaigners, the imprisonment of the three activists highlights the extent of the Egyptian police's resurgence. Police brutality was a major cause of the 2011 uprising, and its continuation under Morsi contributed both to his downfall and to the institution's loss of prestige. But the interior ministry – which runs the police – returned to popularity by backing Morsi's deposition, and appears to believe it has a mandate to crush any kind of dissent, say observers.

"There's nothing new about the police behaving this way, and there's nothing new about them going after activists," said Heba Morayef, Egypt director at Human Rights Watch. "But for me what is significant, and what makes this so ominous, is the sense of entitlement the ministry of interior now has. They're going after the figureheads of the 2011 revolution, and they're trying to erase the gains made since January 2011."

But while the trio's sentencing has enraged Egypt's revolutionaries, it is unclear how much the move will effect the Egyptian street. Maher told the Guardian in November that people were beginning to realise the oppressive nature of Morsi's successors. But he also admitted that many ordinary Egyptians – exhausted by the economic chaos and violence that followed Mubarak's overthrow – were tired of the revolution and were now willing to trade freedom for a government that could bring them political and economic stability.

"I've been out of work for three years, and I just want this country to get better," said Adel Saleh, a bus driver watching a recent 6 April protest. "But 6 April want us to go down."