Bahrain's king has pardoned 1,584 people facing criminal and "riot" charges, state media said Monday, in the largest such mass release in the Gulf nation in years.

The announcement of the royal decree carried by the official Bahrain News Agency (BNA) did not specify whether political prisoners are among those to be released, though a rights group said it was likely.

BNA said that "this royal decree reflects his majesty's keenness to maintain the cohesion and stability of the Bahraini society, while protecting its social fabric."

The pardons cover "those convicted for riot and criminal cases", and were announced as Bahrain's King Hamad bin Isa Al Khalifa marks 25 years since his ascension to the throne, BNA added.

Sayed Alwadaei, advocacy director for the Britain-based Bahrain Institute for Rights and Democracy (BIRD) said political prisoners were likely included in the pardon "as the term 'riot' refers to those who demanded political change".

BIRD said the latest royal decree marks the "highest number of pardoned prisoners since the pro-democracy uprising in 2011," when anti-government protests triggered a state crackdown.

The decree also comes ahead of the Muslim holiday of Eid al-Fitr which marks the end of the fasting month of Ramadan, an occasion that often elicits prison pardons from Gulf leaders.

Bahrain has imprisoned scores of dissidents since the 2011 protest wave, when authorities backed by a Saudi military force crushed Shiite-led demonstrations demanding a constitutional monarchy and an elected prime minister.

In the wake of the Covid-19 pandemic, Bahrain's interior ministry announced in 2020 the release of 1,486 prisoners including 901 who had received royal pardons on "humanitarian grounds".