"We should move forward and not backwards. By putting conditions, we would be going backward," Pakistan Presidential spokesman Farhatullah Babar told PTI.

Asked about the pre-condition set by Singh, Pakistan Foreign Office spokesman Abdul Basit said, "When we have a dialogue we cannot have pre-conditions." Babar insisted that Pakistan had "fully cooperated and is still cooperating" with India in investigating the Mumbai attacks to bring the perpetrators to justice.

Addressing a press conference at the end of the G-20 Summit on Thursday evening at London [Images], Singh said, "India is willing to discuss bilaterally all outstanding issues, including Kashmir. It (Pakistan) has to convince us that it is absolutely sincere in bringing to book the culprits of the attack on Mumbai."

India put the composite dialogue on hold following the Mumbai attacks on November 26 that killed over 180 people. New Delhi [Images] has blamed Pakistan-based elements, including the banned Lashker-e-Tayiba group for the strike and urged Islamabad to bring the perpetrators to justice.

Singh made it clear that discussions with Pakistan cannot proceed if hundreds of people are being killed, as had happened in the case of the Mumbai attacks. The Indian leader said that Pakistan must do everything to bring all culprits involved in the Mumbai terror attack to the book.

"The ball is in the court of Pakistan." Singh was speaking after his maiden meeting with United States President Barack Obama [Images] during which they discussed developments in Pakistan and Afghanistan and cooperation in countering forces of terror.

Obama later said terrorism emanating from Pakistan figured in the discussions as "obviously, we are very concerned about extremists and terrorists who have made camps in the border regions of Pakistan as well as Afghanistan."

At the same time, the US president pushed for Indo-Pak dialogue. "It may make sense to create an effective dialogue between India and Pakistan in this nuclear age and at a time when perhaps the greatest enemy" of the two countries should be poverty, Obama said.

Pakistan welcomed Obama's call for Indo-Pak dialogue.

"We have already called for the resumption of the composite dialogue process without any conditions," Babar said.

"In order to move forward, talks between the two countries should be "resumed at the point at which they were suspended" in the wake of last year's Mumbai terror attacks [Images], he added.

Basit said, "We can't agree more with President Obama as we have been saying the resumption of the composite dialogue is absolutely important and necessary for cooperative engagement and addressing all issues bedevilling our relations. We support Obama's comment."