Medical examiners have concluded that the cause of death for two sisters from Saudi Arabia in New York was a double suicide.

Sisters Rotana Farea, 23, and Tala Farea, 16, had been living in the United States for two to three years when their bodies were found on the banks of New York's Hudson River on October 24.

"Today, my office determined that the death of the Farea sisters was the result of suicide, in which the young women bound themselves together before descending into the Hudson River," said Chief Medical Examiner Dr Barbara Sampson in a statement on Tuesday.

Authorities say the sisters bound themselves together with duct tape and walked into the river, where they drowned.

Because of the way the sisters were found, some feared that they may have been killed.

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Sources told investigators that the Farea sisters had expressed their preference to harm themselves rather than return to Saudi Arabia.

The sisters fled from their home in December 2017 and ended up in a shelter in Fairfax, Virginia, where they had no contact with their families owing to abuse allegations.

In the spring of 2018, Rotana dropped out of George Mason University in Washington, DC, a university spokesperson said.

Tala was a student at Fairfax High School for part of the 2017-2018 school year.

In August 2018, they left the shelter and travelled through Washington, DC, and Philadelphia before arriving in New York City, according to credit card records.

Saudi officials have dismissed media reports that their mother had been ordered to return to Saudi Arabia because Rotana and Tala applied for asylum, saying rather that the mother may have to leave the country because of her immigration status.

The cases of the Farea sisters and Rahaf Mohammed, an 18-year-old Saudi citizen who fled her family, have prompted global attention to Saudi Arabia's strict social rules.

Among the restrictions is the requirement that women have the permission of a male "guardian" to travel, which rights groups say can trap women and girls as prisoners of abusive families.

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Mohammed requested asylum after she barricaded herself in a Bangkok airport hotel room to resist being sent home to her family, whom she accused of abuse.

Her family denied the abuse allegations, but al-Qunun's asylum request was accepted by Canada.

At the time, the UNHCR welcomed Canada's decision and also acknowledged Thailand for giving Mohammed temporary refuge.