The four were killed in an explosion on a tourist bus in the main city occupied Srinagar, minutes after Singh ended a meeting in the same city aimed at restoring peace.
Nobody claimed responsibility for the attack but police immediately blamed Kashmiri freedom fighters. The blast underscored the need for the peace mission by Singh, who earlier met with moderate Kashmiri leaders and on Thursday announced a new group to examine occupied Kashmir's special autonomous status under the constitution.
The working group "will deliberate on matters relating to the special status of (occupied) Jammu and Kashmir within the Indian union," he told a round-table conference with pro-India politicians here. Senior Hurriyat official Moulana Abbas Ansari said the group supported all peace efforts, but the round table would not help.
"It is crowded with people who are part of the Indian system," he said. "As far as the Indian prime minister is concerned, he is very much interested in resolving the issue, but some people around him are not keen about our dialogue process."
Under its accession to India in 1947 upon independence from Britain, occupied Kashmir was granted autonomy over all sectors excluding communications, defence and foreign affairs. But those powers under Article 370 of the constitution have been eroded over the years.
Singh said last year that a resolution of the quarrel over occupied Kashmir could lie in increased autonomy, noting it was the only Indian state with its own constitution.
The group would also "deliberate on effective devolution of powers among different regions to meet regional, sub-regional and ethnic aspirations," Singh said at the close of the two-day meeting on the Himalayan region's future.
There was no immediate reaction from Kashmiri leaders. But they have in the past ruled out autonomy as a solution to the nearly six-decade-old dispute, saying Kashmiris have no desire to stay within the Indian federation.
A key Kashmiri politician also ruled out greater autonomy. "Any solution within the Indian constitution is not acceptable to us," Shabir Shah told AFP.
A strike called by the Kashmiri leaders to oppose the talks closed shops and offices in occupied Srinagar and left streets largely deserted for a second day on Thursday.
They had earlier warned that the roundtable negotiations to halt the unrest were meaningless without their participation. "Unless leaders (armed Kashmiri leaders) are involved in talks, the dream of restoring peace will not be achieved," said a spokesman for Hizbul Mujahedin, the largest freedom fighter group which wants to see Kashmir folded into Pakistan.
The talks were attended by 30 pro-India politicians and boycotted by Kashmiri leaders, but Singh called them "fruitful and engaging". The conference also endorsed the setting up of four other working groups, ones to improve the lives of people, boost the economy and strengthen ties across the heavily militarised Line of Control dividing Kashmir's Indian and Pakistani parts.