NEW DELHI--India's prime minister says the sophistication of the Mumbai siege means the attackers "must have had the support of some official agencies in Pakistan."

Prime Minister Manmohan Singh, meeting with top officials of Indian states, says investigations have made clear that the Pakistan-based group Lashkar-e-Taiba was behind the attack.

Singh did not directly name any Pakistani officials, but India has long blamed Pakistan's powerful spy agency, Inter-Services Intelligence, for being involved in attacks against India in recent years.

Indian leaders have stepped up the rhetoric in recent days about the possible involvement of Pakistani officials in the November siege in Mumbai.