The 2008 attack on Mumbai killed 166 people and strained India-Pakistan relations [AFP]

Four Pakistanis have been charged as co-conspirators in the 2008 attack on Mumbai that killed 166 people, including six Americans, US prosecutors said in Chicago.

The four who were charged on Monday, had been previously mentioned, but not named, in indictments charging American David Headley and Tahawwur Rana, Pakistani-born Chicago businessman, with helping to identify targets in India's commercial capital.

Headley and Rana have also been charged in a plot to attack a Danish newspaper that was never carried out.

Headley pleaded guilty in March 2010 and is cooperating with US investigators about making several trips to India, and later to Denmark, to scout targets for the coordinated and deadly attack.

Rana has been held since his arrest in 2009 as a conspirator with Headley, and his US trial is scheduled to begin on May 16. His attorney was not immediately available for comment.

New indictments

All of the four newly-indicted figures are linked to the Pakistan-based Lashkar-e-Taiba, the armed group that is blamed for the attack on Mumbai.

Those newly indicted were Sajid Mir, Abu Qahafa, Mazhar Iqbal, and a fourth defendant known only by the alias "Major Iqbal."

All four are believed to be in Pakistan.

They were charged with six counts of aiding and abetting the murder of US citizens.

Other charges related to the Mumbai attack included providing support to Lashkar-e-Taiba, identified as a terrorist organisation by the United States.

Mir was also charged in the plot against Denmark's Jyllands-Posten newspaper after it published cartoons of Prophet Muhammad that enraged many Muslims and prompted protests.

Patrick Fitzgerald, US attorney in Chicago, had requested the superseding indictment handed up by a grand jury on April 21 charging the four to be sealed to give the government time to alert US agencies and consult foreign authorities.

The Mumbai attack strained already tense India-Pakistan relations.

India has said it is not satisfied with the pace of Pakistan's investigation, and has demanded more people be put on trial for the attack, including Hafiz Mohammad Saeed, the founder of Lashkar-e-Taiba.