Police said a mother and three children were killed when suspected rebels lobbed hand grenades into the home of Muslim civilian Abdul Aziz after he refused to open the door to militants in southern Doda district early yesterday.

Aziz and three others were injured in the attack, a police spokesman said.

"The motive for the killings was not known," he said.

People in Doda town later staged a protest against the attack, witnesses said.

About 800 people took part in the demonstration as shops and businesses closed, they said.

In neighbouring Anantnag district, suspected rebels overnight stormed into another Muslim household, wounding the owner and killing his wife.

"They (militants) abducted his student son and later hanged him to death," the spokesman said.

In the state's summer capital Srinagar suspected militants overnight shot dead a Muslim contractor, police said.

No group claimed responsibility for the civilian deaths.

Muslim rebels often target people they suspect of collaborating with Indian security forces or the government.

Meanwhile, Indian troops shot dead four militants, three of them members of the hardline Lashkar-e-Taiba rebel group, in the districts of Rajouri, Anantnag and Pulwama overnight, police said.

Srinagar, a hotbed of militancy, and Jammu, the winter capital -- the main population centres -- are due to stage municipal polls on Tuesday.

Security has been tightened in Srinagar and Jammu, which for the first time will elect mayors, police said.

"We have tightened security ahead of tomorrow's voting," a police officer, Javed Ahmed said.