From Kathy Quiano, CNN
Grim search under way in Indonesia
Rescue workers have not found any survivors so far in plane wreckage in Indonesia
Officials have recovered 12 bodies from the mountainside
The Russian Sukhoi Superjet 100 started to descend and then vanished off radar screens
Russia and Indonesia will conduct an investigation into the crash
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Jakarta, Indonesia (CNN) -- Troublesome weather conditions hampered recovery efforts Friday as teams combed a steep mountainside where a Russian jetliner crashed on a demonstration flight in Indonesian this week.
Twelve bodies were found early in the day, according to Vice Marshal Daryatmo, head of the National Search and Rescue Agency. Daryatmo, who like many Indonesians uses only one name.
The Sukhoi Superjet 100 came to rest on the side of Mount Salak, a volcano south of Jakarta, after disappearing from radar screens on Wednesday.
President Susilo Bambang Yudhoyono announced a joint investigation on Friday after a phone call with his Russia counterpart Vladimir Putin.
"We both agreed to work together to investigate and analyze what happened. This cooperation has started although the operations should not stop,even without with this cooperation," the Indonesian leader said. "I welcome the offer from Russian President Putin because the goal is to investigate what could have caused the plane crash."
The Russian Investigative Committee has said that 48 people were on board the plane, including eight Russian crew members. But the Russian news agency RIA-Novosti said the number was 45, citing Sukhoi Civil Aviation President Vladimir Prisyazhnyuk as saying three of the people on the passenger list did not board the flight.
The wreckage was spotted at an elevation of about 5,800 feet (nearly 1,800 meters).
The cause of the crash remained unclear. The Russian Investigative Committee said it had launched a criminal probe into possible safety violations.
The plane was on a demonstration flight for Indonesian Ministry of Transportation officials and representatives of Indonesian airlines, the Russian Embassy in Jakarta said before the crash.
Indonesia's Sky Aviation signed a $380 million deal in 2011 to buy 12 Sukhoi Superjet 100s, and press reports said a number of Sky employees were on the plane that went down. Sukhoi employees are also among the missing.
It was the first crash of a Sukhoi Superjet 100, RIA-Novosti said.
The plane was on its second demonstration flight Wednesday when it lost contact with air controllers at Jakarta's Halim Perdanakusuma Airport.
The Sukhoi jet arrived in Jakarta as part of a demonstration tour of six Asian countries. It had been to Myanmar, Pakistan and Kazakhstan, and was scheduled to visit Laos and Vietnam after Indonesia, RIA-Novosti said.
Sukhoi manufactures military aircraft and is known especially for its fighter jets. Its civilian aircraft is narrow-bodied with a dual-class cabin that can transport 100 passengers over regional routes. It flew its maiden flight in 2008.
In March, a Superjet 100 operated by Russia's Aeroflot Airlines was forced to abandon its flight to Astrakhan, Russia, and return to Moscow because of problems with the undercarriage, according to RIA Novosti.
A similar defect in another Aeroflot-operated Superjet 100 plane had to be fixed in Minsk in December.
Russia's state-run United Aircraft Corp. said the defect did not affect passenger safety.
CNN's Alla Eshchenko in Moscow contributed to this report.
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