The American network quoted the official as saying that the warning was issued not once but 'twice'. A second government source told ABCnews.com that specific locations, including the Taj Hotel, were listed in the US warning.
"US intelligence indicated that a group might enter the country by water and launch an attack on Mumbai, said the official, who refused to be identified due to the ongoing investigation into the attacks and the sensitivity of the information," the CNN added.
"Indian security forces have confirmed to CNN that not only did US officials warn them of a water-borne attack in Mumbai -- they were told twice. The area entered a higher state of alert for a week, including tightened security measures at hotels, but those efforts were eventually reduced, Indian officials said," the network, which repeatedly broadcast the story last evening, maintained.
On Nov 18, Indian intelligence also intercepted a satellite phone call to a number in Pakistan known to be used by a leader of the terror group Lashkar-e-Taiba, believed to be responsible for the weekend attack, Indian intelligence officials were quoted as saying by ABCnews.com. The Indian intercept also revealed a possible sea-borne attack, it said, citing officials.
Since last Friday, US intelligence agencies have been tracking the phones and SIM cards recovered by Indian authorities from the terrorists involved in Mumbai attacks leading to a "treasure trove" of leads in Pakistan and several possible connections to the US, officials told he TV network.
Officials said one of the cell phone SIM cards may have been purchased in the US but would not provide any more details because of the ongoing nature of the investigation, ABCNews said.
The phones also include the same "Thuraya Satellite" phone intercepted in November by Indian intelligence agencies, the report said.
The United States National Security Agency, the report said, has the technical means to retrieve all calls made from satellite and cell phones in south Asia region.
"Once we have the number we will be able to know everyone who was called and where the calls were made from," one former intelligence office told the network.
A US counter-terrorism official was quoted as saying all leads continue to point at Lashkar-e-Taiba, a Pakistan-based terrorist group with strong ties to al-Qaeda. The group has taken credit for a number of previous terror attacks, including the Mumbai commuter rail system and the Indian Parliament building.