Bahrain's king Sunday ordered the citizenship of 551 Bahrainis to be restored, after his country was harshly criticised by the UN and rights groups for revoking people's nationalities.
"His Majesty King Hamad bin Isa Al Khalifa has issued an order, reinstating the citizenship of 551 convicts whose nationality had been revoked as per court rulings," state-run Bahrain News Agency reported.
US ally Bahrain has been gripped by bouts of unrest since 2011, when authorities cracked down on Shiite-led protests demanding political reform.
Since then, hundreds of protesters have been jailed and those convicted of terrorism offences have been stripped of their nationality.
Bahrain has accused Iran of training and backing demonstrators in order to topple the government, charges Tehran denies.
BNA news agency said King Hamad, who can reverse court decisions, requested that the competent authorities take into account "the nature of crimes committed".
He has instructed the interior ministry to examine each case and prepare a list of those whose nationalities can be reinstated.
Human rights groups estimate that 990 mainly Shiite people have had their citizenship revoked since the start of judicial proceedings in 2012 against those who took part in the protests.
Ruled for more than two centuries by the Sunni Al-Khalifa dynasty, Bahrain has a majority Shiite Muslim population, according to unofficial estimates contested by the government.
Sunday's decision comes after a Bahraini court on Tuesday sentenced 138 people to prison terms and revoked their citizenship, at the end of a mass trial denounced by rights group Amnesty International.
Those convicted -- Shiite Bahraini citizens, according to a judicial source -- belonged to a group of 169 people accused of forming a "terror" group with links to Iran's Revolutionary Guards.
- 'Serious concerns' -
This was the biggest group of people to have been convicted and to have lost their citizenship as a result of a single trial since 2012, according to the Bahrain Institute for Rights and Democracy.
The UN High Commissioner for Human Rights on Thursday expressed alarm about the court's decision.
"Tuesday's convictions give rise to serious concerns about the application of the law, particularly through a mass trial that reportedly lacked the procedural safeguards necessary to ensure a fair trial," rights commissioner Michelle Bachelet said in a statement.
"Deprevation of nationality must not be arbitrary, especially on discriminatory grounds," she said, stressing that "arbitrary deprivation of nationality places the individuals concerned and their family members in a situation of increased vulnerability to human rights violations."
Bahraini authorities have repeatedly denied taking discriminatory measures against citizens of the kingdom, and say they are facing violence from Iran-backed groups despite denials from Tehran of any involvement.
Since 2011 all opposition groups have been banned and disbanded.
In January, Bahrain's supreme court upheld a life term against Sheikh Ali Salman, the head of the main Shiite opposition group Al-Wefaq, for allegedly spying for rival Qatar.
Prominent rights defender Nabeel Rajab in December lost his final appeal against a five-year jail term for writing tweets deemed offensive to the state.
And last year King Hamad signed off on a decree allowing military courts to try civilians accused of "terrorism".