The only surviving suspected gunman in the Mumbai terrorist attacks retracted his confession today, saying it was extracted through coercion.

On the opening day of his trial in Mumbai, a lawyer representing Mohammed Ajmal Amir Kasab told a special court that he wanted to withdraw the statement, which had been made under duress.

The lawyer, Abbas Kazmi, said: "My client has said he was tortured and that the confession was forced. He therefore wants to retract it."

The judge, ML Tahiliyani, said the court would pass an order on the validity of the confession on Saturday.

Prosecutors say Kasab, who sat barefoot in the dock dressed in a full-sleeve T-shirt and navy blue trousers, was one of the gunmen who arrived in Mumbai by sea from Pakistan to carry out the attacks in which 166 people were killed.

The special public prosecutor Ujwal Nikam told the court there was "prima facie evidence" of a criminal conspiracy "hatched in Pakistan to attack India". He said at least one Pakistani military officer was involved in the attack and its sophistication suggested the involvement of Pakistan's intelligence agency.

Kasab, a Pakistani, is charged with 12 criminal counts, including murder and waging war against India. Prosecutors say Kasab and nine other gunmen who were killed during the siege are responsible for the deaths of 166 people and injuring 304 more.

"There was a criminal conspiracy hatched in Pakistan to attack India," Nikam said, with the "ultimate target of capturing Jammu and Kashmir, which is part and parcel of India".

The prosecutor vowed to get to "the root of terror" and said the identity of all those involved would be revealed through the ongoing investigation.

He told the court the attacks in November were masterminded by the Muslim militant group Lashkar-e-Toiba with the help of at least one Pakistani military officer. Nikam said the plot was made possible by a "terrorist culture" that had taken root in Pakistan.

Lashkar-e-Toiba is widely believed to have been created by Pakistani intelligence agencies in the 1980s to fight Indian rule in Kashmir. The Himalayan region of Kashmir, which is divided between India and Pakistani but claimed by both, has long been at the centre of bitterness between the two countries.

Pakistani officials have acknowledged that the Mumbai attacks were partly plotted on their soil and announced criminal proceedings against eight suspects. They have acknowledged that Kasab is Pakistani but have repeatedly denied any involvement by their intelligence agencies in the atrocity.

Kasab's two co-defendants, Faheem Ansari and Sabauddin Ahmed, are Indian nationals charged with helping to plot the attacks. Their lawyer maintains that they are innocent.

Court officials have said they hope the case will be finished in six months to a year. The trial for India's deadliest terror attack, the 1993 Mumbai bombings that killed 257 people, took 14 years to complete.