The violent frenzy that continued Thursday in India's financial capital, killed at least 101 people and injured more than 300, including six foreigners, reports said.
"There are indications that the perpetrators of the crime, who arrived in Mumbai by boats, are Pakistani nationals," the sources told PTI.
They said the information was gathered from some of the captured terrorists.
Separately, R.R. Patil, deputy chief of Maharashtra state, told PTI it would not be wise to reveal detailed information on the attacks.
"We have total clues. But disclosing information would not help the case. This is an attack on the country. We will disclose information at an appropriate time," he said.
CNN reported some Indian news outlets had received e-mails saying a group calling itself the Deccan Mujahedeen took responsibility for the attacks, but it was not able to verify the reports.
One Indian TV channel reported two boats with explosives and arms had been found, indicating the gunmen may have come by sea to enter the city.