"We have dispatched 500 FC (Frontier Constabulary) troops in Karachi," Interior Minister Rehman Malik told reporters in Islamabad.
Violence erupted after provincial minister Zulfiqar Mirza, from the main ruling Pakistan People's Party, criticised its ex-coalition partner, the Muttahida Qaumi Movement (MQM) and its exiled leader Altaf Hussain.
Mirza later said in a statement that those remarks were his "personal opinion" and "if someone was hurt by them then I apologise".
The MQM last month quit the PPP-led coalition that governs the country and the southern province of Sindh, of which Karachi is the capital.
The party has now called for nationwide protests over Mirza's criticism.
Home ministry official Sharafuddin Memon said that the death toll stood at 14, whilst 21 people were injured and more than a dozen vehicles had been set ablaze in different parts of the city.