The U.S. Pacific Command told Fox News Wednesday that it could not confirm reports of possible sightings of a U.S. Marine helicopter that disappeared Tuesday while conducting disaster relief operations in Nepal.

Nepali officials said the helicopter -- carrying six Marines and two Nepali troops -- reportedly was spotted north of the country's capital, Kathmandu.

“We have been told it was spotted in Tamakoshi region,” Interior Ministry spokesman Laxmi Dhakal told the Deutsche Presse-Agentur press agency late Tuesday. “But until [our] choppers make landing and get to it, we still can’t say anything about its condition or of its passengers.”

A Nepali military official separately said Wednesday that the helicopter appeared to have come down in the rivers that run through valleys east of Kathmandu.

"The info we have is that it is down in one of the rivers, but none of the choppers has seen it yet," Major Rajan Dahal, second-in-command of the Barda Bahadur Battalion, told Reuters in Charikot, a village where the missing Huey was scheduled to land and deliver aid.

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But a spokesman for the U.S. Pacific Command, which is coordinating the search effort, told Fox News that nothing has been found yet. 

"We still remain optimistic here and in Nepal," the spokesman said.

Pentagon Spokesman Col. Steve Warren said Wednesday that flights were suspended for the day due to darkness. 

Warren added the search remains a "search and rescue" operation, not a recovery. 

Earlier Wednesday, U.S. Air Force pararescuemen joined the search for the helicopter. The 3rd Marine Expeditionary Brigade tweeted photographs of the so-called "PJs" boarding helicopters to begin their search-and-rescue missions.

Warren said Tuesday there were "no indications of a crash," because the area is rugged. No emergency beacon was detected.

Other aircraft nearby heard the helicopter's pilot say something about a "fuel problem."

The aircraft is part of Marine Light Attack Helicopter Squadron 469. It had just dropped off supplies at one area and was en route to a second location.

Charikot was one of the villages hardest hit by a 7.3 magnitude quake Tuesday that killed 37 people, Reuters reported. Nepal is still struggling to recover from a devastating quake nearly three weeks ago that left more than 8,000 dead.

Fox News' Lucas Tomlinson and The Associated Press contributed to this report.