Egyptian authorities released two activists and a journalist Sunday after months in pre-trial detention, officials and lawyers said, amid concern by President Joe Biden's administration over the arrest and harassment of government critics.

State security prosecutors ordered the release of the three late Saturday pending ongoing investigations into charges against them, according to two judicial officials. They spoke on condition of anonymity because they were not authorised to brief the media.

Esraa Abdel-Fattah, a pro-democracy activist and writer, walked free early Sunday, her sister Shimaa wrote in a Facebook post. She was a co-founder of the April 6 movement that played a crucial role in the 2011 pro-democracy uprising that toppled longtime autocrat Hosni Mubarak.

Abdel-Fattah was arrested in October 2019 in a city west of Cairo, during a crackdown that followed small but rare anti-government protests. Hundreds were arrested at the time, but many were later released.

She faces charges of spreading false news, being a member of a banned group and misuse of social media, but despite the lengthy detention has yet to stand trial, according her lawyers.

Authorities also released journalist Gamal el-Gamal, said rights lawyer Nasser Amin. El-Gamal is widely known for his columns critical of the government of President Abdel Fattah el-Sissi. Amin posted a photo on Facebook showing him sitting with el-Gamal at home after his release.

Security forces arrested el-Gamal in February upon arrival at Cairo International Airport from Turkey, where he had lived since 2017.

El-Gamal was charged with spreading false news, joining a terrorist organisation and inciting public opinion against state institutions.

Authorities also released Abdel-Nasser Ismail, deputy head of the Socialist People's Alliance Party, after roughly two years in pre-trial detention, his brother Abdel-Mawla Ismail said.

Ismail was arrested in the September 2019 crackdown. He was accused of spreading false news and of joining a terrorist organisation.

The releases came after an outcry by rights advocates when prosecutors last week referred Hossam Bahgat, a leading Egyptian investigative journalist and human rights advocate, to trial.

Bahgat said he was accused of insulting Egypt's election authority, spreading false news alleging electoral fraud, and using social media to commit crimes.

The accusations stem from a tweet Bahgat wrote last year blaming the election authority's chairman for allegedly mishandling last year's parliamentary vote, according to the Egyptian Initiative for Personal Rights, or EIPR, the organisation Bahgat founded 18 years ago.

U.S. State Department spokesman Ned Price condemned Bahgat's indictment and the detention and harassment of Egyptian civil society leaders, academics, and journalists under el-Sissi.

“We've communicated to the Egyptian government our strong belief that individuals such as Hossam Bahgat should not be targeted for expressing their views peacefully,” Price said last week.

“As a strategic partner we've raised these concerns with the Egyptian government, and we will continue to do so going forward.”

The Egyptian government has in recent years waged a wide-scale crackdown on dissent, jailing thousands of people, mainly Islamists, but also secular activists involved in the 2011 Arab Spring uprising that toppled longtime autocrat Hosni Mubarak.

Journalists have also been targeted, with dozens imprisoned and some foreign journalists expelled.

Egypt remains among the world's top jailers of journalists, along with Turkey and China, according to the Committee to Protect Journalists.