Police in the Indian city of Bangalore are on high alert amid fresh security fears, two days after a fatal attack on a college professor.
Bangalore police say they are taking no chances with new threats
Prof MC Puri was killed and four other scientists wounded when a gunman opened fire during a conference at the city's Indian Institute of Science.
The chief minister of Karnataka state has blamed "terrorists" but it is still not clear who was behind the attack.
On Thursday, newspaper offices received a threat to launch more attacks.
A letter faxed to the media and signed by a man named Moinuddin claimed that six attackers would target a hotel and the residence of the chief minister which is next door.
Police Commissioner AK Singh said the warning appeared dubious but officers would take no chances.
Police have also released a computer-generated sketch of the gunman based on eyewitness accounts.
They are looking for a man aged between 20 and 30 and say they think he acted alone.
On Friday a large number of mourners attended the cremation of Prof Puri in Delhi.
Bangalore is a hub for hi-tech businesses and security has been stepped up outside major installations in the city and across India.
Relatives of Prof Puri ahead of Friday's cremation in Delhi
"It is a matter of grave concern," federal home secretary VK Duggal told Associated Press.
"An alert has been sounded at all the establishments engaged in scientific, defence and nuclear activities," he said.
The BBC's Habib Beary in Bangalore says police have made no breakthroughs but suspect the involvement of terrorist groups in Wednesday's attack.
"The intention is to create fear and demoralisation," Karnataka Chief Minister Dharam Singh told reporters on Thursday.
"They are terrorists and we are trying to identify who they are."
Police believe the attack on the conference, attended by about 300 delegates from India and abroad, was aimed at getting international publicity.
Bangalore is home to more than 1,500 information technology companies, many of them global, accounting for one-third of India's software exports.
A large number of friends, relatives and colleagues attended the funeral of Prof Puri.
Son Saurav performed the last rites at the funeral pyre in front of Prof Puri's wife Raksha and daughter Shelley.
Prof Suresh Chandra, acting head of Prof Puri's mathematics department at Delhi's Indian Institute of Technology, told the Press Trust of India: "His sudden death is a big blow to the field of science and research, particularly to the IIT."