December 1, 2008 -- U.S. intelligence agencies warned their Indian counterparts in mid-October of a potential attack "from the sea against hotels and business centers in Mumbai," a U.S. intelligence official tells ABCNews.com.
A second government source says specific locations, including the Taj hotel, were listed in the U.S. warning.
One month later, 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 responsible for the weekend attack, Indian intelligence officials say.
The Indian intercept also revealed a possible sea-borne attack, the officials say.
The chairman of the company that owns the hotel, Ratan Tata, told CNN that security was temporarily increased following a warning.
Tata told CNN Sunday that the enhanced measurers were later eased and, in any case, "could not have stopped what took place."
Since Friday, U.S. intelligence agencies have been tracking the phones and SIM cards recovered by Indian authorities from the Mumbai terrorists leading to a "treasure trove" of leads in Pakistan and several possible connections to the United States, officials say.
Officials say one of the cell phone SIM cards may have been purchased in the United States but would not provide any more details because of the ongoing nature of the investigation.
The phones also include the same Thuraya satellite phone intercepted in November by the Indian spy agency RAW, the Research and Analysis Wing, which runs an extensive electronic intercept operation.
NSA, the National Security Agency, has the technical means to retrieve all calls made from satellite and cell phones in the south Asia region.
Officials say one of the phones recovered was a Thuraya satellite phone.
"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 says.
A US counter-terrorism official says all leads continue to point Lashkar e Taiba, a Kashmir separatist group with strong ties to al Qaeda.
The group, referred to as LeT in the Indian press, has taken credit for a number of previous terror attacks on India targets, including the Mumbai commuter rail system and the Indian Parliament building.
"They share training, weapons and coordinate targets with al Qaeda," says former CIA intelligence officer John Kiriakou, an ABC News consultant.