Officials were unsuccessful in a daylong search for the missing U.S. Marine helicopter that disappeared after being dispatched in Nepal. The UH-1Y Huey helicopter was reported to have been missing just hours after another massive 7.3 magnitude earthquake hit Nepal on Tuesday.

Maj. Gen. John Wissler, head of the U.S. military's joint task force in Nepal, believes that the mountainous terrain of the country poses the biggest challenge to the rescue efforts, according to ABC News.

"It's just a matter of receiving the signal... Where they went down, whether it got damaged during the set-down process ... there are a number of reasons why those beacons and so forth would not operate," Wissler said.

The U.S. helicopter disappeared while delivering supplies to Dolakha, one of the districts that was hit the hardest by the new earthquake, according to Reuters. Six U.S. Marines and two Nepali soldiers were onboard the aircraft when it lost contact.

Together with six Nepali helicopters, about 400 soldiers failed to locate the missing aircraft in a grueling 21-hour search.

"There is no positive confirmation of any sighting of the aircraft, and we have no communication with them at this moment," said Captain Cassandra Gesecki, spokeswoman of the Marines.

Visiting an army base in Charikot, retired Nepali army general Bala Nan Sharma discussed the progress of the search for the missing UH-1Y helicopter.

"If it just landed in that forest, it would be lost. Only helicopter pilots who have the eye will be able to find it. This terrain is very beautiful, but very difficult," he said.

Nepal Home Ministry official Laxmi Prasad Dahal fears that the ongoing search for the helicopter is preventing valuable resources for relief from reaching the earthquake-damaged country, Reuters reported.

"The work of sending relief and rescuing the injured people to hospitals has been delayed due to this," he said.