UPDATE 1-U.S. says Pakistani-based group likely hit Mumbai

(Adds details, more quotes)

BRUSSELS, Dec 2 (Reuters) - A group partly or completely based in Pakistan may have been responsible for the attacks by militants in India's financial hub of Mumbai which killed 183 people, a senior State Department official said on Tuesday.

"There are a lot of reasons to think it might be a group, partially or wholly a group, that is located on Pakistan's territory," the official told reporters on the sidelines of a meeting of NATO foreign ministers.

The official, who did not identify the source of his information, spoke hours before U.S. Secretary of State Condoleezza Rice was to leave Brussels for New Delhi to discuss last week's attacks in Mumbai with the Indian government.

The official, who spoke on condition of anonymity, pointed to Pakistani government statements that if the attack originated on its territory then the government would be prepared to pursue the attackers there.

"They have promised to be willing and committed to following up and pursuing it," said the official. "They accept the possibility that there might be people located on Pakistani territory," he added. "We all need to trade information and pursue every possible lead."

The official declined to provide the source for his suspicions or to name the group, except to say that it was based on a "variety of information from various sources, some of it public, some of it not."

Investigators have said the attacks were carried out by militants trained by the Pakistan-based Lashkar-e-Taiba group, which is blamed for a 2001 attack on India's parliament.

Asked whether it could be the Lashkar-e-Taiba group, he replied: "That has to be a possibliity."

Asked about reports that U.S. intelligence agencies had warned India of the possibility of an attack on Mumbai, the official replied: "No. I am not in a position to confirm that. I am not in a position to comment on U.S. intelligence." (Reporting by Sue Pleming; Editing by Richard Balmforth)