Washington: The Khorasan group of the ISIS or the ISIS-K, which operates in south Asia, last year attempted a suicide attack in India, a top American official has told lawmakers.

In fact, of all the branches of the ISIS, ISIS-K is the outfit that is of the most concern to the US, Russel Travers, Acting Director of the National Counterterrorism Center, Office of Director of National Intelligence, said on Tuesday.

"Of all of the branches and networks of ISIS, ISIS-K is certainly one of those of most concern, probably in the neighbourhood of 4,000 individuals or so," Travers said in response to a question from Indian-origin Senator Maggie Hassan.

"They have attempted to certainly inspire attacks outside of Afghanistan. They attempted last year to conduct a suicide attack in India. It failed," Travers said when Hassan asked about the ability of ISIS-K to carry out terrorist attacks in the region.

Hassan had travelled to Afghanistan and Pakistan last month, during which she said she heard firsthand the concerns of the US military about the growing and very real threat of ISIS-K, the ISIS affiliate in Afghanistan.

"I heard clearly that ISIS-K threatens not only US forces in Afghanistan, but also has designs on striking the US homeland," she said.

Last week, Travers had said that there were more than 20 ISIS branches globally, some of which are using sophisticated technology such as drones to conduct operations.

Despite America's key victories against the ISIS in Syria and Iraq, the terror outfit remains a deadly threat to the United States, Senator Hassan said.

Travers said ISIS-K tried a couple of years ago to inspire an attack in New York but the FBI interrupted. Then there was an attack in Stockholm in 2017 that killed five people, he added.

"So they certainly have a desire and the propaganda would indicate that they want to conduct attacks outside of Afghanistan as far relatively limited," the counter-terrorism official said.

According to Travers, after 9/11, the US was primarily focused on an externally directed attack capability emanating from a single piece of real estate along the Afghanistan-Pakistan border.

"Eighteen years later, we face a homegrown violent extremist threat, almost 20 ISIS branches and networks that range from tens to hundreds to thousands of people, al-Qaeda and its branches and affiliates, foreign fighters that flocked to Iraq and Syria from well over 100 countries, Iran and its proxies, and there is a growing terrorist threat from racially and ethnically motivated extremists around the globe," he said.

By any calculation, there are far more radicalised individuals now than there were at the time of 9/11, Travers told the lawmakers.

"This highlights the importance of terrorism prevention. While some aspects of the threat can only be dealt with through kinetic operations, the residents of the ideology will not be dealt with by military or law enforcement operations alone. The world has a lot of work to do in the non-kinetic realm to deal with radicalization and underlying causes," he added.

Travers also said that al-Qaeda retains its long-standing ties to the Haqqani Network and other militant networks active in Afghanistan and Pakistan that frequently target US personnel.