Police said militants fired a rifle grenade and opened fire on police camp at Imam Sahib, 52 kms from Srinagar, around 3.15 pm.
ASI Sethi Ram was killed and three others, including a Central Reserve Police Force jawan, sustained injuries.
Injured constable Abdul Hamid of IRP first battalion, Special Police Officer Mohammad Shafi and CRPF jawan A Hatu were shifted to Srinagar for treatment.
The condition of the SPO was stated to be "critical". Police and CRPF personnel fired in retaliation, but the militants escaped. A hunt had been underway for the ultras.
However, no militant outfit has claimed responsibility for the attack, a police spokesman said.
The offensive comes barely a week after normal activities resumed in the South Kashmir district town which was rocked by widespread protests for 47 days over the alleged rape and murder of two women on May 30.
Earlier on June 23, the then Deputy Inspector General of Police (South Kashmir), Rajesh Kumar escaped a bid on life when militants attacked his cavalcade at Mamender while returning from Shopian after taking stock of the situation.
The attack had left one of his police guards injured.
Bodies of 17-year-old Asiya and her sister-in-law Neelofar Jan (22) were recovered from Shopian on May 30, a day after they went missing from their orchard.
After the incident, Shopian was rocked by strikes till July 16 when the special investigation team (SIT) arrested four suspended police officers, including the then Superintendent of Police Javid Iqbal Mattoo for "destroying evidence" in the case.
Police officers were suspended on the recommendations of the one-man judicial commission of Justice Muzaffar Jan on June 22, a day after he submitted the interim-report.
The commission in its final report also had referred to involvement of some "agencies of state police" in the rape-murder case, but had not identified any.