The US also called on Pakistan to end immediately its support and safe haven provided to all terrorist groups operating on its soil.
"We are working closely with the government of India in terms of getting to the bottom of the terrorist attacks," US Ambassador to India Kenneth Juster told reporters here.
Noting that the US had been cooperating with India on the issue of terror, he said, "We have condemned them; we have previously condemned terrorist sanctuaries that exist in Pakistan and we have suspended military assistance to them"
"This incident bolsters our resolve to cooperate with India on counterterrorism matters and work with them to get to the bottom of what occurred last week," he said on the Pulwama incident, in which 40 CRPF personnel were killed in one of the deadliest terror strikes in decades in Jammu and Kashmir.
Juster described the Pulwama attack as "horrific."
Pakistan-based Jaish-e-Mohammad (JeM), headed by Masood Azhar, has claimed responsibility for the attack in which a suicide bomber rammed a vehicle carrying explosives into a bus in the CRPF convoy.
The US ambassador is here leading a high-level US delegation for the five-day Aero India event beginning here Wednesday with the largest-ever US participation in Asia's premier air show.
Asked if he would foresee Pakistan ordering a crackdown on terror groups operating from its soil with more pressure from the US, Juster said "I don't want to get ahead of the situation that is developing, we have condemned the existence of terrorist sanctuaries and we are urging Pakistan to crackdown on those and we will have to see what the factual... in terms of exactly how this incident occurred."
On US' defence relationship with India, Juster said it continued to undergo a rapid expansion as part of the deepening strategic partnership between the two countries.
He said the US and India were committed to strengthening defence cooperation in line with India's status as a major defence partner and added that defence acquisition was a key element of "deepening our bilateral relationship."
The US delegation to Aero India includes deputy under secretary of defense for acquisition and sustainment Alan Shaffer and director of the defense security cooperation agency lieutenant general Charles Hooper.