A helicopter chartered by conservation group World Wildlife Fund with 24 people aboard including an American aid worker, a Finnish diplomat and a Nepalese minister went missing Saturday in Nepal's mountainous east, officials said.

Civilian and army helicopters had been searching the area in eastern Taplejung district where the Russian-built MI-17 helicopter disappeared early Saturday. But they called off the search due to poor weather, the rescue unit at Katmandu airport said. Foot patrols combing through the dense foliage were also called off at dusk until dawn Sunday.

The helicopter carrying 20 passengers and four crew left Ghunsa village but never arrived at its destination in Suketar village, the rescue unit said in a statement. The flight was supposed to last 20 minutes. Both villages are in the Taplejung district, a mountainous area covered with thick forests about 310 miles east of Nepal's capital, Katmandu.

CountryWatch: Nepal

The World Wildlife Fund said the 20 passengers were on their way back from a conservation site at Ghunsa and seven staff members from the organization were among the missing.

The passengers included Nepal's Forest Minister Gopal Rai and his wife, the Finnish Embassy Charge d'Affaires Pauli Mustonnen and Deputy Director of the U.S. Agency for International Development in Nepal, Margaret Alexander, WWF said in a statement on its Web site. Seven WWF employees were also among the missing, including four Nepalis, Australian Jill Bowling, Canadian Jennifer Headley and American Matthew Preece, it said.

Several Nepali journalists, other government officials and two Russian crew members were also on board, it said.

"We hope that all on board will be rescued safely," WWF International's Director General James Leape said in a statement. "Our thoughts are with our missing colleagues and their families and WWF is doing everything it can to help the government of Nepal in its search for the helicopter."

The helicopter was chartered from Shree Helicopter Co., company officials said.