SAN JOSE, Costa Rica - Investigators are looking into what caused a charter aircraft to crash in woods in the country's northwest soon after takeoff, killing the 10 US citizens and two local crew members on board.

Officials said on Sunday evening that they were still seeking to establish the names of the US citizens 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.

"The government of Costa Rica profoundly regrets the deaths of 10 US passengers and two Costa Rican pilots in the air accident," Costa Rican President Luis Guillermo Solis said in a statement.

A family in the suburbs of New York said five of the dead were their 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 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 on Sunday from Punta Islita on a planned flight to the capital 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.