Romanian search teams and Israeli representatives arrived at the crash site in a remote, mountainous area on Tuesday morning. An Israeli military statement said that no survivors were found and that the search was ongoing.
Earlier, an Israeli military official in Jerusalem said all on board were believed to be dead.
"We have reason to believe that all seven crew are dead," said Brig. Gen. Relik Shafir, a reserve officer with the Israeli air force. "It's been a black day for all of us."
Mircea Opris, Romania's chief mountain rescue official, said the chopper had burst into flames after it hit a mountain in a remote area.
Ciprian Aldea, a spokesman for the local police, said human remains and helicopter parts were scattered across the area.
"Corpses, as such, have not been found. It is a very difficult area, very rocky," he said. "You can't reach the area without the appropriate search equipment."
Shafir, the Israeli officer, said two experienced Israeli three-man flight crews and one Romanian liaison officer had been on board the chopper.
He said two Israeli CH-53 helicopters had been training in a mountainous area in heavy fog when one of the helicopters lost touch with the other and apparently hit the mountain.
On Tuesday, the Israeli air force sent an Israeli C-130 Hercules aircraft plane to Romania to help search for the Israeli helicopter.
Israel's military has been training with the Romanians since 2004. The Israelis also train with other European militaries and with the U.S. to give their crews experience in unfamiliar terrain.
Associated Press writer Matti Friedman in Jerusalem and Alina Wolfe Murray in Bucharest contributed to this report.