A liberal Muslim scholar, accused of blasphemy for a speech he gave during a visit to the United States, was shot and killed in Karachi on Thursday. The scholar, Muhammad Shakil Auj, was the dean of Islamic studies at the University of Karachi. Dr. Auj was shot in the head and neck and died immediately, officials said.

Dr. Auj, 54, had earlier complained to the police about death threats he began receiving after delivering a speech in the United States in 2012, his colleagues and the police said.

Nasir Lodhi, a senior police official, said that Dr. Auj told the police that four professors at the University of Karachi had accused him of blasphemy for comments he made during that speech. Mr. Lodhi said he could not say where the speech was made, or the nature of the offending comments.

Dr. Auj lodged a criminal complaint against the four professors, who were later arrested by the police. One of them, Dr. Abdul Rasheed, had previously held Dr. Auj’s position as dean of Islamic studies at the university. The four men face trial but are currently free on bail, the police said.

Around the same time, a religious seminary in Karachi issued a fatwa against Dr. Auj, accusing him of blasphemy and calling for his death.

The New York Times reported that a week earlier, a visiting religious scholar at the same Islamic studies department, Maulana Masood Baig, was also shot dead by unknown attackers.