Bahrain has arrested four American citizens, accusing them of entering the country under false pretenses and participating in "attacks on police," according to a police statement released Monday.

In the statement, officials said that three men and one woman who "had not registered with the concerned authority and were involved in illegal activities," were detained on Sunday in Sitra, south of the capital, according to CNN.

The officials went on to allege that one of the four journalists "was wearing a mask and participating in attacks on police alongside other rioters in Sitra." 

"At least some of the arrestees were in the country as members of the international media but had not registered with the concerned authority and were involved in illegal activities," the statement said, without elaborating on what those activities were, according to the Associated Press.

Officials declined to respond to questions about the arrests, but it was confirmed that they occurred amid violent protests marking the anniversary of the kingdom's 2011 uprising. The uprising in question was driven by the country's Shiite majority, who demanded greater political rights from the Sunni-led monarchy. It is regarded as the largest of the Arab Spring wave of demonstrations to rock Gulf Arab states.

Bahrain's government has since introduced a series of reforms, but low-level unrest, particularly in Shiite communities, still continues. Small groups of activists frequently clash with riot police, and bombs occasionally target security forces.

The Human Rights Watch describes the incident and others like it as indicative of the "highly problematic" human rights situation in Bahrain. The group argues that authorities use "disproportionate force to quell unrest," while peaceful protesters are imprisoned and stripped of citizenship while officials are not held to account for allegations of torture and other crimes.  

In the meantime, the local U.S. embassy said it was aware of the situation but unable to comment further due to privacy-act concerns.