Riyadh: Saudi Arabia plans to execute more than 50 people convicted of terrorism, two Saudi newspapers reported this week, in what appears to be a warning to would-be jihadists at a time of militant attacks on the kingdom.

Fifty-five people were awaiting execution for "terrorist crimes" that killed more than 100 civilians and 71 security personnel, the newspaper Okaz reported on Thursday, without specifying when the executions would occur.

On Monday, the semi-official newspaper al-Riyadh reported that 52 people would be put to death soon, but it later pulled the story from its website without explanation.

Some of those facing execution were affiliated with al Qaeda, Okaz said. Others are from Awamiya, a largely Shi'ite 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 Shi'ites convicted after protests.

Awamiya residents responded to the news by closing off roads leading into the city with burning debris, local activists said.

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 $1.5 million 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.

Saudi Arabia has already executed over 150 people this year, mostly by public beheading, the most in 20 years, rights group Amnesty International said this month.

The Saudi monarchy has in recent years sentenced to death dozens of people convicted of taking part in al Qaeda attacks in Saudi Arabia from 2003-06 and again in 2009.

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 Shi'ite Muslim minority as well as security officers and Western expatriates.

The Syria and Iraq-based militant group has 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.

Saudi courts have also to death this year seven Shi'ite men convicted of sedition, for taking part in pro-democracy protests and attacks on police during demonstrations over discrimination from 2011-13.

Two of those men were minors at the time of the protests. Sentencing them to death to having bodies publicly displayed prompted an international outcry.

The last time Saudi Arabia carried out mass executions for security offences was after a group of Islamist militants seized Mecca's Grand Mosque in 1979.

The only people executed so far for al Qaeda attacks in the kingdom in the last decade, which have killed hundreds, were two men from Chad earlier this year.