Amnesty International has expressed alarm at reports that the authorities in Saudi Arabia are planning to execute dozens of people in a single day, reported BBC.

The newspaper Okaz said 55 people were awaiting execution for “terrorist crimes”, while a now-deleted report by al-Riyadh said 52 would die soon, without specifying when the executions would occur.

They are thought to include Shia who took part in anti-government protests.

A statement from Amnesty said that given the spike in executions this year, it had no option but to take the reports very seriously.

The group believes at least 151 people have been put to death in Saudi Arabia so far this year – the highest recorded figure since 1995.

Some of those facing execution were affiliated with al-Qaeda, Okaz said. Others are from Awamiya, a largely Shiite town in the oil-producing Eastern Province where the government has suppressed demonstrations for equal rights.

Diplomats in Riyadh say their governments have been assured Saudi Arabia will not execute Shiites convicted after protests.

The alleged al-Qaeda militants stand accused of attempts to overthrow the government and carry out attacks using small weapons, explosives and surface-to-air missiles, Okaz said.

One prisoner was accused of trying to buy nuclear material in Yemen worth US$1.5 million (NZ$2.08m) for use inside Saudi Arabia.

The charges against the Awamiya residents include sedition, attacks on security officials and interference in neighbouring Bahrain, which has also experienced unrest since 2011.

According to Reuters, Islamic State sympathisers have killed dozens in Saudi Arabia over the past 12 months with a string of mosque bombings and shootings aimed at members of the Shiite Muslim minority as well as security officers and Western expatriates.

The Syria and the Iraq-based militant group have called on its followers in Saudi Arabia to stay home and conduct attacks there instead of travelling to join the caliphate it declared in 2014.

Saudi police have detained hundreds of the group’s suspected sympathisers and have joined an international coalition carrying out air strikes against it in Syria. Riyadh has also deployed state-affiliated clergy to denounce jihadist ideology.

In 2014, the total number of executions carried out was reported to be 90.