Jailed Karachi Mayor and MQM leader Waseem Akhtar and deputy mayor Arshad Vohra, also of the MQM, took oath on Tuesday, DawnNews reported.
Akhtar opened his speech with a slogan of "Long live Muttahida, long live Bhutto and long live Imran Khan."
"We have to set aside our differences," Akhtar said.
After stepping away from the mic, Akhtar once again took to the podium to express support for the MQM. "We will work together for Karachi and Sindh," he said.
His statement comes just days after Farooq Sattar, senior MQM leader, announced that the party was dissociating itself from party chief Altaf Hussain and the London office following Hussain's anti-Pakistan speech which sparked violent protests in Karachi.
"Long live Karachi, long live Sindh, long live Pakistan," he said.
Akhtar is among four mayors and 200 chairmen of as many municipal bodies across Sindh province who took oath of their offices on Tuesday.
That Akhtar would be able to take his oath remained uncertain even in the hours before the ceremony as his attendance depended on a production order allowing him to do so.
District judge Imdad Hussain Khoso withdrew an order he had issued on Monday in this regard as he did not have clearance from the Sindh High Court to administer oath at the ceremony.
Almost immediately, a returning officer for the KMC then requested jail authorities to produce the jailed mayor-elect and arrange security so he could attend the oath-taking ceremony.
Akhtar is the first person in the country to have won the mayoral election from prison with a comfortable margin against his rival candidate pitted by a six-party alliance formed to contest against the the MQM.

Source: Arab News