Mumbai attacks co-accused David Coleman Headley has testified that he received espionage training against India from Pakistan's spy agency Inter-Services Intelligence (ISI).

"ISI did provide me (espionage) training," Headley told a Chicago court as he was grilled by the defence attorney Charles D. Swift on the third day of the trial of Pakistani-Canadian Tawahhur Rana, another co-accused in the 26/11 attacks, in a Chicago court.

The statements formed part of the testimony of Headley, who has pleaded guilty.

These disclosures, which further cements India's charges that elements of ISI were involved in the Mumbai attacks, is also corroborated by information given by federal prosecutors in the documents to the court, which were unsealed on Wednesday.

The ISI training to Headley was provided by Major Iqbal, who was his ISI handler, in a two-storey safe house in Lahore near the airport, the Mumbai terror suspect told judges during the course of questioning by Swift.

Headley told the court that when he met Major Iqbal in 2006, he expressed dissatisfaction at the military and espionage training that he had received from the Lashkar-e-Tayyaba earlier.

Major Iqbal told him that the training received from LeT was "not very good" and was "very elementary", so he decided to give instructions to him.

Headley told the defence attorney that this training in espionage against India was given to him in Lahore on the streets and a safe house near the airport.

It was a two-storey house in a residential neighbourhood and there was a small compound outside the house, Headley said when pressed by Swift during the closing hours on the third day of the trial.

Despite repeated questioning, Headley said that he didnot know the full name of Major Iqbal, but was sure that he was from the ISI.

He was introduced as Major Iqbal to him.

Although Major Iqbal was never seen by Headley in military uniform, he came to meet him several times in a military jeep and his subordinates had military designations, Headley said.

Headley said he never went to the ISI headquarters and added that he was introduced to Major Iqbal by military personnel, a fact corroborated by the unsealed document.

In this unsealed document federal prosecutors said in 2006, Headley traveled to the FATA area with Pasha.

"During the trip, Headley and Pasha were stopped and questioned by Pakistani authorities. Headley was questioned by an individual who identified himself as Major Ali. He told Ali about his training with LeT, Ali then asked Headley for his contact information.

"Several days later, Headley was contacted by an individual who identified himself as Major Iqbal," said the unsealed document.

"Over the next several years, as described in more detail below, Headley met with Major Iqbal and his associates many times. During these meetings, Headley was trained in various topics, including spotting and assessing people, recognizing Indian military insignia and movements, dead drops and pick up points, and clandestine photography," the unsealed documents said.

When questioned by Swift, Headley told the court that both the ISI and Major Iqbal trained him for espionage against India.

He was expected to go to India, make contacts.

The ISI and Major Iqbal were particularly motivated by the fact that he was US born and an American national, this would have concealed his real identity in India.

"They (ISI and Major Iqbal) wanted me to have a business so as to have the ability to have a long tern stay in India. In discussion with them I suggested it to take the help of Dr Rana's (Tahawwur Rana) business to get this objective," Headley said.