The victims were returning Jaipur after attending a marriage function in Haryana when the incident occurred late last night, SHO Shahpura police station Amir Hasan said.
Two of the deceased identified as Kailash and Suresh were police constables posted at Assistant Commissioner of Police (ACP) Jhotwara (Jaipur) office.
Third deceased was identified as Bajrang Takhar, he said.
"All the four injured are being treated in critical condition," he added.