"Countries found wanting in their commitment to zero tolerance of terrorism will be made to pay heavy price by the international community," Pranab Mukherjee, India's foreign minister, said in New Delhi on Monday.
"Our diplomatic efforts in dealing with terrorist states will continue unabated."
Indian officials are frustrated at what they see as Pakistan's slowness at arresting the attack's alleged planners.
They want the new US administration to press Islamabad to act on a dossier of evidence presented this month by New Delhi.
Earlier, Indian police were granted two more weeks to hold and question Mohammed Ajmal Kasab, alleged by New Delhi to be the lone survivor from a group of 10 suspected attackers.
An Indian court extended Kasab's police custody on Monday until February 2.
Rakesh Maria, a senior Mumbai police official, had previously said that Indian police was "quite hopeful" of bringing formal charges against Kasab before January 24 - 60 days after his initial detention.
Meanwhile, in Islamabad, Shah Mehmood Qureshi, the Pakistani foreign minister, and the government's highest interior ministry official, Rehman Malik, briefed foreign diplomats on Pakistani efforts since the attack.
Malik set a 10-day deadline on the weekend for an investigating team to complete a report and on Monday promised "good news in two weeks", according to a Western diplomat who attended the meeting.
Pakistan has detained scores of members of Lashkar and an affiliated Islamic charity, the Jamaat-ud-Dawa, but India is demanding it dismantle what it calls the "infrastructure of terrorism".
Pakistan has been angered by the Indian suggestion that Pakistani state agencies were involved and what it sees as repeated Indian hints of military action.