BOMBAY, India -- India warned Saturday that attacks like the deadly Bombay train bombings are jeopardizing its peace process with nuclear rival Pakistan, and demanded an "unambiguous" response from the Group of Eight summit.

Authorities began randomly frisking commuters, and installed closed-circuit television cameras at six busy train stations, saying all stations eventually would be monitored.

Investigators rounded up more than 300 people for questioning in connection with the attack on Bombay's commuter train network, but freed most of them later.

The eight explosions during Thursday's evening rush hour killed at least 200 people, provoking a groundswell of public anger -- and accusations that the perpetrators were Islamic militants aided by Muslim-majority Pakistan, the neighbor and archrival of predominantly Hindu India.

Foreign Secretary Shyam Saran told reporters that terrorist attacks are eroding the India-Pakistan peace process, which began in 2004.

"Every time something like this happens it undermines public confidence (in the peace process)," Saran said. "Anger is generated. So obviously this becomes a question mark over the process."

"As a result of these terrorist attacks it is becoming very difficult to take the process forward," he said.

Pakistani Foreign Ministry spokeswoman Tasnim Aslam declined comment.

Indian Prime Minister Manmohan Singh said Friday that the bombers had support from inside Pakistan, and told Islamabad to rein in terrorists. Pakistan dismissed the allegations as "unsubstantiated."

Singh, set to fly to St. Petersburg Sunday to observe the Group of Eight summit of major industrialized nations, will make "a very strong pitch for a united response" to the bombings, Saran said.