The incident came to light after the letter dated November 7, 2012, addressed to the Consul General based in Mumbai, was forwarded to the Ministry of External Affairs by the Saudi Arabian Ambassador.
The Economic Offences Wing has registered a case under sections 420 (cheating), 468 (forgery for the purpose of cheating) and 471 (using a forged document as genuine) of Indian Penal Code, a senior police official said.
In the forged letter, the official said, the Consul General has been allegedly requested to facilitate visa for one Abdul Sattar and his family to visit Mecca and Madina.
Malay K Singh, Joint Secretary in the Ministry, said in the complaint that the letter was forged as well as the Minister's signature.
"The Minister was on tour abroad on November 7, 2012. Signature itself is incorrect. It is usually not the practice for the Minister to address a letter to Consul Generals based in India," the complaint said.
Singh said Khurshid has instructed that a First Information Report be lodged and the matter investigated. Police said a probe is on in the case.