CAIRO (Reuters) - A coalition of secular and leftist Egyptian groups on Monday slammed the arrests of opposition figures and called for the release of all such prisoners not convicted of violent offences.

Masoum Marzouk, a former ambassador, and six other activists were arrested on Thursday and detained for 15 days pending investigation on charges of joining a terrorist group and receiving funds for terrorism. He had recently called for a referendum on President Abdel Fattah al-Sisi’s rule, in rare public criticism of the former general.

The Civil Democratic Movement (CDM) said in a statement read out by its spokesman, Yehia Hussain, at a news conference that the group “rejects such police tactics in dealing with political opponents”.

“The recent campaign of arrests ... is part of a systematic policy followed by the regime to silence any voice that opposes its oppressive policies that are hostile to freedoms,” the statement said.

The statement said such policies were a “cover-up for its economic and social failures by constantly claiming that there are conspiracies that are being woven in the dark against the country”.

Egyptian authorities have jailed thousands of opponents in recent years, most of them suspected Islamists, but some secular activists and journalists. The government has said its actions are directed at terrorists and saboteurs trying to undermine the state.

Sisi was elected president in 2014, a year after the military ousted Islamist president Mohamed Mursi following mass protests against his rule.

The CDM, founded in December, includes eight secular and left-leaning parties and 150 prominent activists and political figures. It called for a boycott of the presidential election in March after all major opposition campaigns withdrew on the grounds of intimidation.

Former presidential candidate Hamdeen Sabahi, a member of the movement who ran in the 2012 and 2014 elections, called the government a “failed regime”.

“This regime must be changed,” he said. “This authority is a failure. This authority is repressive ... an authority of corruption, tyranny and repression is an oppressive regime,” he told the news conference.

Fareed Zahran, head of the Egyptian Democratic Social Party, said the target of the call for regime change was not Sisi, but rules and regulations that shackle freedoms.