India's Prime Minister Narendra Modi has vowed to punish those responsible for what he called a "despicable" and "cowardly" attack on an army base in Indian-administered Kashmir.
The military says at least 17 soldiers and four of the attackers were killed in the September 18 pre-dawn assault in the town of Uri.
Officials said an unspecified number of militants carrying guns and grenades infiltrated across the de factor border with Pakistan before attacking the base.
No group has claimed responsibility.
But Indian Home Minister Rajnath Singh wrote on Twitter that he was “deeply disappointed with Pakistan's continued and direct support to terrorism and terrorist groups."
"There are definite and conclusive indications that the perpetrators of [the] Uri attack were highly trained, heavily armed and specially equipped," he also said.
Indian military officials said all four gunmen killed were "foreign terrorists," and that initial investigations suggested they belonged to Jaish-e-Mohammed, a Pakistan-based militant group that has been active in Kashmir for more than 15 years.
Pakistan rejected allegations that it was involved, with Foreign Ministry spokesman Nafees Zakaria saying, "India immediately puts blame on Pakistan without doing any investigation."
The attack comes as the Himalayan region has seen its largest anti-India protests in recent years since the killing on July 8 of a popular rebel commander by Indian troops.
More than 80 people have been killed in clashes between residents and security forces.
The Muslim-majority region is divided between India and Pakistan, but most people in the Indian portion favor independence or a merger with Pakistan.