The fighters killed two soldiers during the ambush and then attacked a police jeep when it arrived, killing one policeman.
Kashmiri fighters ambushed an Indian military convoy in Kashmir on Wednesday, killing three personnel amid intensified protests against the killing of a field commander of Pakistan-based Hizbul Mujahideen.
Police superintendent Imtiaz Hussain said the fighters ambushed an army convoy early on Wednesday in the town of Baramulla, killing two soldiers, and then struck at a police jeep when it arrived, killing one policeman.
"We were aware about their presence around Baramulla town for over a month but due to violence across Kashmir, they managed to consolidate and carry out an attack," Hussain said.
At least 64 protesters have been killed and thousands injured during 40 days of unrest, while schools, shops and offices remain closed in much of Kashmir as paramilitary troops patrol.
Indian security forces killed five protesters and injured 10 on Tuesday.
The turmoil has raised tension with Pakistan which invited India for talks on the disputed territory, drawing an angry rebuke from India.
The nuclear-armed neighbours, which have fought three wars since independence in 1947, both claim the Muslim-majority region in full, but rule it in part.
UN monitors remain on the heavily fortified border between the two sides in Kashmir.
On Wednesday, Indian authorities re-imposed a curfew in the summer capital, Srinagar, to stop a separatist alliance of political and religious groups from holding a sit-in outside the office of the UN Military Observer Group to press for its involvement.
"The UN cannot watch the massacre in Kashmir as a mute spectator," said Mirwaiz Umar Farooq, the chairman of a faction of the All Parties Hurriyat Conference.
The UN group routinely declines to comment to media, referring queries to UN headquarters.
India accuses Muslim Pakistan of supporting Kashmiri fighters while Pakistan accuses India of meddling in Pakistani trouble spots.
Pakistan denies giving material support to Kashmir fighters and denounces rights abuses in Indian Kashmir.