Terming as a 'very positive step' the response by Pakistan to the Mumbai attack evidence dossier provided by India, the United States on Thursday said it shows that Islamabad is serious in bringing the perpetrators of the terror strikes to justice.

"We have asked Pakistan, and India has asked Pakistan, to cooperate fully in trying to bring to justice those who are responsible for the Mumbai attacks. So this would certainly be a very positive step," State Department spokesperson Robert Wood said.

Pakistan on Thursday admitted for the first time, after a series of flip-flops, that the 26/11 Mumbai attacks were 'partly' plotted on its soil and launched from its shores for which it has arrested six persons.

"So let me just leave it at that. It's a good step. I'll have to find out more details about the arrests. But I think it shows that Pakistan is serious about doing what it can to deal with the people who may have perpetrated these attacks," Wood said.

"I don't have much more in the way of detail with regard to the arrest, but Pakistan has committed that it would do everything in its power to bring people to justice, who may have committed these atrocities, who have been within their borders," he said.