Israel's Supreme Court upheld on Tuesday a more than three-year-old detention without trial of a Palestinian suspected of being an al Qaeda biological weapons expert.

Samer al-Baraq was born in Kuwait, studied microbiology in Pakistan, underwent military training in Afghanistan and was recruited in 2001 to al Qaeda by Ayman al-Zawahri, who is the group's leader today, according to Israeli prosecutors.

They said he was planning attacks against Israelis.

Al-Baraq, who is 39 and has family in the Israeli-occupied West Bank, denies the allegations and had asked the Supreme Court to free him. A three-justice panel rejected the appeal.

Citing Israel's concerns about the threat al-Baraq could pose if released, the court said in its ruling that "at this time there is no less damaging way of mitigating this danger" than his continued detention.

Israel often holds suspected militants without trial, based on evidence presented in closed security courts. It says the practice pre-empts militant attacks against it while keeping counter-intelligence sources and tactics secret.

According to a court document, al-Baraq was once detained and questioned in the United States and was later jailed in Jordan for five years. He was arrested in 2010 at Jordan's Allenby bridge crossing with the West Bank, Israel says.