Singh was in Kashmir to meet members of pro-Indian political parties ahead of state elections.
'Willing to talk'
The prime minister expressed sadness over the deaths and reiterated India's commitment to finding a solution to the Kashmir issue through dialogue.
"We are willing to talk to anyone," he said.
In recent months Kashmir has seen some of the largest protests against Indian rule in two decades.
Tens of thousands of people have been killed in Kashmir since armed revolt against New Delhi's rule broke out two decades ago.
The separatist alliance, the All Parties Hurriyat (Freedom) Conference, has called for more protests and a strike on Saturday.
"Kashmir's problem is neither of laying railway links, nor providing economic packages or power projects," Mirwaiz Umar Farooq, the chairman of Hurriyat, said.
"It is the question of political aspirations of the people."
Singh is due to inaugurate the first train service in the Kashmir Valley on Saturday.
Earlier, Singh, accompanied by Sonia Gandhi, leader of the ruling Congress party, inaugurated a 450-megawatt hydroelectric project on the Chenab river, which flows from Indian Kashmir into Pakistan, in the district of Doda.
Pakistan has objected the Baglihar dam, saying it will limit its access to water.
India has rejected the charge and says the project is crucial for power-starved Kashmir.
But Singh insisted that India had taken "special care" in addressing Pakistan's concerns.