US investigators have dismissed a report that computer hackers were behind the failure of a water pump at a plant in the midwestern US state of Illinois.

Chris Ortman, a spokesman for the Department of Homeland Security, said "detailed analysis" by DHS and the Federal Bureau of Investigation "found no evidence of a cyber intrusion" at the water facility in Springfield, Illinois.

"There is no evidence to support claims made in initial reports -- which were based on raw, unconfirmed data and subsequently leaked to the media -- that any credentials were stolen, or that the vendor was involved in any malicious activity that led to a pump failure at the water plant," he said.

"Analysis of the incident is ongoing and additional relevant information will be released as it becomes available," the DHS spokesman added.

Joe Weiss, an infrastructure control systems expert with consultant Applied Control Solutions, reported the alleged hacking attempt last week, citing a disclosure by the Illinois Statewide Terrorism and Intelligence Center (STIC).

According to Weiss, the disclosure by the state organization said a vendor of Supervisory Control and Data Acquisition (SCADA) software was hacked and customer usernames and passwords stolen.

There are about a dozen or so firms that make SCADA software, which is used to control machines in industrial facilities ranging from factories and oil rigs to nuclear power and sewage plants.

The IP address of the attacker was traced back to Russia, Weiss cited the STIC disclosure as saying.

Ortman, the DHS spokesman, said, however, that the DHS and FBI "have concluded that there was no malicious traffic from Russia or any foreign entities, as previously reported."

Weiss, in a blog post late Tuesday, said the DHS statement "appears to conflict with the STIC report and its positive statements that an event had occurred."

"If DHS turns out to be correct in its assumptions, then anyone acting on the STIC warning would have been wasting precious resources addressing a problem that doesn't exist," Weiss said.

While dismissing the report of a hacking attack on the Illinois plant, a senior DHS official said the department and FBI were looking into a separate hacking claim at another US utility.

In that incident, a hacker claimed to have accessed an industrial control system responsible for water supply and posted images allegedly obtained from the system, the official said.