A soldier and three Kashmiri fighters were killed when troops raided a rebel hideout in the southern district of Rajouri, police said.
In the summer capital Srinagar, suspected rebels set off explosives, as a bus packed with soldiers passed by on a major highway, senior police officer Muhammad Amin said.
At least 33 troops and a woman passer-by were injured in the blast, which could be felt two kilometres away, he said.
Kashmir's largest rebel group Hizb al-Mujahidin claimed responsibility for the attack in a telephone call to a local newspaper.
The bus was travelling to Srinagar from the northern town of Baramulla as part of a convoy, an army officer at the scene of the blast said.
The explosion caused minor damages to another army vehicle and a few civilian cars and led to a suspension of traffic on the busy road, causing a large traffic jam.
Police said the explosives were kept near a locked shop which
was razed to the ground by the impact.
Last week, a woman was killed and 10 other people injured in a similar explosion on the same highway.
The explosion is one of the most significant attacks on Indian troops since the militaries of India and Pakistan entered into a ceasefire on their borders in Kashmir on 26 November.
Both Indian security forces and the rebels have said that the truce does not affect their operations inside Indian-administered Kashmir.
At least 180 people have died in the insurgency during the border ceasefire.
The nearly 15-year Kashmir insurgency has claimed more than 40,000 lives according to the official count. Separatists put the toll between 80,000 and 100,000.