Pakistani prosecutors charged seven men on Wednesday with planning and helping execute last year's Mumbai terror attacks, AP reported.
The indictments came on the eve of the first anniversary of the attacks on India's financial center that killed 166 people.
All seven suspects in the case pleaded not guilty, defense lawyer Hammad Amin Siddiqui and prosecutor Malik Rab Nawaz told The Associated Press by telephone.
The men, allegedly belonging to the Lashkar-e-Taiba militant group, could face the death penalty if convicted.
The trial is a key test of Pakistan's vow to punish those responsible for the Nov. 26-28 attacks on hotels, a train station and other targets.
Proceedings are taking place behind closed doors at a maximum-security prison not far from the capital, Islamabad.
Lawyers for the suspects have said they are unable to disclose any details of the charges against the men, who have appeared in court for pre-indictment hearings in recent months.
Two of the defendants, Zaki-ur-Rehman Lakhvi and Zarrar Shah, have been publicly accused by India of masterminding the attacks.
India, the United States and other Western countries are closely watching Pakistan's efforts to punish the suspects.
In the past, Islamabad has failed to punish militants suspected of attacks on targets in its giant eastern neighbor, with which it has fought three wars since independence from Britain in 1947.
Pakistan's intelligence agencies are known to have funded and trained Islamist militants to use as proxies against the much larger Indian army in the disputed region of Kashmir. The government says it no longer does this, but many Pakistanis remain sympathetic to the militants' aims.