Police arrested a top official of Liberia's main opposition Congress for Democratic Change overnight as the capital was under curfew after rioting by unpaid government workers, party sources said Saturday.
The police have given no reason for the arrest of CDC secretary general Acarous Gray, but local media reports suggested that he is suspected of inciting the violence.
The CDC denied the allegation, calling for his immediate and unconditional release.
Information Minister Cletus Sieh told AFP he had no details of the arrest, adding that he would be going to police headquarters to find out about it.
CDC leader Winston Tubman commented, "We are surprised. We are shocked over the arrest of Mr. Gray and we want him to be released unconditionally."
"I can't make any further comment because the situation in the country is very tense now," he added.
The CDC on Friday pulled out of an inter-party dialogue to sweeten relations with the government following the disputed November 8 presidential election won by incumbent Ellen Johnson Sirleaf after Tubman withdrew, claiming fraud.
The government imposed a curfew on Monrovia Friday after a second day of protests by thousands of rampaging part-time workers over pay delays.
Clashes broke out at a Monrovia sports complex, a stadium and a high school where the workers, youths who had done part-time work for the government, were asked to assemble to receive their pay.
There were reports of widespread damage to government buildings and vehicles across the city, as well as private properties.
A 10:00 pm to 6:00 am (2200 to 0600 GMT) curfew will remain in place as long as needed, Sieh told AFP earlier.
"The government is cautioning people to stay off from the streets during curfew hours because state security personnel will arrest and deal with anyone caught in violation of this order," he said.