Costa Rican investigators are working into what caused a charter aircraft carrying 10 U.S. citizens and two local crewmembers to crash in a wooded area in the country's northwest soon after takeover, killing everyone on board.

Officials said Sunday evening that they were still seeking to establish the names of the Americans who died when the plane went down at midday in Guanacaste. They said Nature Air had provided a passenger list, but the names on it had not been confirmed.

A family in the suburbs of New York City said five of the dead Americans were relatives on vacation. They identified them as Bruce and Irene Steinberg and their sons Matthew, William and Zachary, all of Scarsdale.

"We are in utter shock and disbelief right now," Bruce Steinberg's sister, Tamara Steinberg Jacobson, wrote on Facebook. She also confirmed the deaths in an interview with NBC News.

Rabbi Jonathan Blake of the Westchester Reform Temple in Scarsdale said in a statement posted on the Temple's Facebook page and sent in an e-mail to The Associated Press that the Steinbergs were involved in philanthropy and local Jewish groups. "This tragedy hits our community very hard," Blake wrote.

At a news conference, Enio Cubillo, director of Costa Rica Civil Aviation, said the Nature Air charter flight crashed shortly after taking off just after noon Sunday from Punta Islita on a planned flight to the capital of San Jose. He said investigators were looking into possible causes.

Cubillo identified the pilot as Juan Manuel Retana and described him as very experienced. Former Costa Rican President Laura Chinchilla said via Twitter that Retana was her cousin.

The same plane had arrived in Punta Islita on Sunday morning from San Jose and was delayed in landing by strong winds, Cubillo said.

Nature Air did not respond to phone and email messages.