The Egyptian Popular Current stated on Thursday that security forces have surrounded the group's office in Mansoura, where many injured protesters are sheltering, and are refusing to allow medical aid into the building.
According to a Thursday statement by the opposition group, there are dozens of people inside the office suffering from asphyxiation, due to the numerous volleys of teargas fired Wednesday night during clashes at the building.
Clashes erupted after the Central Security Forces attempted to disperse protesters who had been staging marches across the city to muster support for a planned civil disobedience campaign.
"Security forces, with the help of the Brotherhood and its member Saber Zaher, have been following private cars who have been volunteering to save the injured," read the statement.
"The current will however continue its support for ongoing calls for civil disobedience and will endorse any move that seeks to press ahead with the demands of the revolution."
Three members of the current were arrested during clashes that erupted across the city over the past few days.
According to an Ahram Online reporter in Mansoura, which is the capital of Daqahliya governorate, clashes were ongoing from Monday until late on Wednesday between security officers, hundreds of anti-government protesters and a handful of journalists, in the vicinity of the governorate headquarters.
Police fired teargas and birdshot at stone-throwing protesters.
Calm, however, descended on the city Thursday morning.
Meanwhile, Egypt's Socialist Popular Alliance Party alleged that security forces stormed the party's headquarters in Mansoura late on Tuesday where those injured during violent clashes with police were being treated.
In a Wednesday statement, the party asserted the "right of Egyptians to peacefully strike and protest against the Brotherhood hegemony," and renounced "the use of violence and repressive measures against angry protesters who seek to push ahead with the demands of the revolution."
The party urged the police to repudiate that strategy of "turning a blind eye to crimes" carried out by what it described as "the Brotherhood militias."
It also called upon protesters to avoid violence which is used as an ostensible reason to "tarnish the image of the revolutionaries."
For its part, Egypt's Nasserist Karama Party in the governorate of Daqahliya has also condemned the violent crackdown on protesters.
In a Wednesday statement, the party held the interior ministry responsible for recent clashes in Mansoura.
It also deplored the indiscriminate arrest of "peaceful protesters," including Islam Fouad, a member of the party and the Egyptian Popular Current.
Daqahliya, north-east of Cairo, has been the flashpoint of unrest in the past few days, with sporadic clashes breaking out between police and anti-Brotherhood protesters.
Political discontent has been growing over what opposition sees as a return of Mubarak-era heavy-handed tactics.
Calls for the campaign in Daqahliya governorate came along the lines of a similar drive in the canal city of Port Said.
The move was provoked by anger over the death sentences handed down to 21 Port Said residents for their involvement in last year’s Port Said stadium disaster, in which scores of rival football fans were killed.
The verdict triggered violent riots across the canal city, which led to clashes with police in which at least 40 people were killed and 250 injured.
On Sunday, hundreds went on strike and blocked off main roads in the Nile Delta city of Mahalla in the adjacent Gharbiya governorate as part of a parallel civil disobedience drive.