ISTANBUL — Turkish investigators have extended their inquiry into the suspected assassination of a dissident journalist by Saudi Arabian officials to three areas in or near Istanbul, a Turkish official said on Friday, while police officers and prosecutors questioned Turkish employees of the Saudi Consulate in the city.

Looking for evidence of the fate of the journalist, Jamal Khashoggi, who was last seen more than two weeks ago entering the consulate, investigators were searching the Belgrad forest, a wooded area just north of Istanbul; Pendik, a district on the Asian side of the city; and a rural residence in Yalova, a town 60 miles south of the city, the official, who spoke on the condition of anonymity, told The New York Times. Turkish officials have alleged that Mr. Kashoggi was tortured, killed and dismembered inside the consulate, accusations the Saudi government has denied.

Fifteen Turkish employees of the consulate, including the consul’s driver, testified in a court in downtown Istanbul on Friday, the state-run news agency Anadolu reported. Earlier this week, investigators searched the consulate and the consul’s nearby residence, though officials noted that there had been plenty of time to eliminate evidence, and that the consul had left the country, returning to Saudi Arabia.

Using surveillance television recordings and GPS signals, the authorities have tracked the movement of consular vehicles on Oct. 2, the day Mr. Khashoggi, a Saudi journalist living in the United States, disappeared, looking for his remains or other evidence of what happened to him. The police retrieved video recordings from the Belgrad forest area, and Turkish investigators were looking into the possibility that one of the Saudi officials whom the Turks have accused of killing Mr. Khashoggi and of disposing of his body owned a property in Yalova, the news agency Ihlas said.