The bomb threat to the Indian embassy here was made by a caller from the western United States city of Utah by a man speaking in "Hinglish", indicating that he was apparently of South Asian origin, sources said on Wednesday.
The bomb threat prompted the evacuation of the embassy premises, chancery and Ambassador Nirupama Rao's residence.
Giving more details about the threat, police and US Secret Service said a suspicious object was found inside the premises of the chancery.
The suspicious object, found on Tuesday morning, was later declared to be harmless, sources told PTI on condition of anonymity.
Preliminary investigations revealed that the call to the Indian embassy was apparently made from Utah. It is believed that the caller had used VOIP (voice over internet protocol) to make the call to the embassy around 10:30 in the morning.
According to sources, the caller in his/her brief message to the Indian embassy was speaking in "Hinglish" indicating that the caller is apparently of a South Asian descent.
The US Secret Service, which is investigating the incident, said the investigation is still on and they are looking into every possibility.
The Secret Service along with the Metropolitan Police Department of District of Columbia were very prompt in reaching the Indian Embassy as soon as they were informed about the call.
Areas around the Indian embassy and the Chancery was immediately cordoned off and thorough search was conducted by the Secret Service, Metropolitan Police along with a bomb disposal squad and the fire department.
Portions of the busy Massachusetts Avenue -- on which houses the Indian embassy and the Chancery -- were closed for about 90 minutes, a Secret Service spokesman said, adding that they did not find any harmful object during the search operation.
As a precautionary measure, the residence of the Indian Ambassador to the US, Nirupama Rao, was searched. Rao was not at her residence at that time. She was on her way to Indiana.
"Anonymous caller claimed bomb placed in our Emb this morning. Police called in. Thorough check done. Nothing found. All our personnel safe," Rao tweeted on Tuesday.
State Department spokesperson Victoria Nuland later told reporters that all the three Indian properties in Washington DC were "evacuated and checked" after the bomb threat call.
"Security officials have declared them (premises) cleared. No device was located. I think there'll be an investigation, obviously, and we'll see what that leads to," she said.
"I would guess that part of our evaluation going forward in terms of what happened will be to determine whether the security posture is adequate," Nuland said when asked if the incident would lead to increase in security in and around the Embassy premises in Washington.
"The security authorities arrived promptly and conducted a thorough on-site inspection of the building and concluded that there were no findings to suggest any bomb threat. The embassy has resumed its normal functioning," the Indian embassy said in a statement.
A few months ago, the security at the embassy was increased and metal detectors were installed for the screening of every visitor to its premises.
Meanwhile, at the Chancery there is no visible security measure. The portion of the basement which is open to the general public for their passport and related services, there are no security guards stationed. However, close circuit television cameras have been in place for quite some time.
Unlike the American system, wherein it has a full-fledged security division at all its diplomatic missions -- and at most of the places marines are placed on duty -- the security strength at the Indian embassy in Washington, sources said, is about half-a-dozen and that too they are said to be peon grade staffers rather than those from the nation's security forces.