Bahrain has accused wealthier neighbour Qatar of harming its national security by "luring" some nationals to take Qatari citizenship, state news agency BNA said, a charge that could widen a rift among Gulf Arab countries.
Bahrain, Saudi Arabia and the United Arab Emirates recalled their ambassadors from Doha in March, accusing Qatar of failing to honour an accord not to interfere in each others' internal affairs. The countries are all members of the Gulf Cooperation Council (GCC), along with Kuwait and Oman.
Efforts to patch up the rift, largely centred around Qatar's backing for the Islamist Muslim Brotherhood movement which the other countries deeply oppose, have so far failed.
BNA quoted the Interior Ministry's Undersecretary for Nationality, Passports and Residence Affairs, Sheikh Rashid bin Khalifa Al-Khalifa, as saying Qatar had "targeted specific families and singled out a particular category of people" with no consideration to Bahraini laws.
"The naturalisation of Bahrainis would affect Bahrain's national security and vital interests negatively," the agency said on its English website late on Wednesday, quoting the official.
Sheikh Rashid gave no details on who was being targeted for naturalisation or how many had been granted Qatari citizenship.
Bahrain is acutely sensitive to changes in its demographic balance between Shi'ite Muslims and Sunnis.
The Sunni-ruled kingdom has a Shi'ite majority and an ongoing conflict between the government and predominantly Shi'ite protesters calling for more democracy has strong sectarian elements.
There was no immediate comment from Qatar on the accusation, but a Gulf source said Bahrain's complaint was linked to requests for naturalisation by some Bahraini families with tribal links to Qatar.
These requests are still under consideration, the source said, and the applicants had not yet met the requirement that include residing in the country for five years before being granted citizenship.
The source speculated that Bahrain may be concerned because such moves could affect its demographic balance.
"The problem with Bahrain is keeping a Sunni-Shi'ite balance and that's why this issue is very sensitive for them," the source told Reuters.
Bahraini Shi'ites have long accused their government of naturalising Sunnis from abroad so that they would eventually outnumber Shi'ites in the small Gulf kingdom.
Bahrain, home of the U.S. Fifth Fleet, still sees regular violence more than three years after security forces quelled pro-democracy protests that erupted on the island during the Arab Spring.
Bahrain's opposition has been largely decimated by arrests and prosecutions, and some young men have increasingly turned violent, targeting police and security forces with home-made bombs. Many are in jail and some are on trial on charges related to attacking security forces.
In the latest trial, BNA said that the criminal court in Manama decided on Wednesday to revoke the citizenship of nine Bahrainis convicted of "forming a terrorist cell".
The cell had intended to smuggle weapons into Bahrain and help some detainees flee the country, BNA said.
The court also sentenced 14 people to prison terms ranging from five to 15 years for the same charges, BNA said, adding that some of them were also found guilty of contacting elements who work for non-Arab, Shi'ite power Iran.