The executive director of Human Rights Watch and another senior staff member were denied entry to Egypt for "security reasons" after being held at the Cairo airport for 12 hours, two of the group's staff said on Monday.

Kenneth Roth and Sarah Leah Whitson had flown to Cairo to take part in publication of a report to be released on Tuesday on the mass killings of protesters by security forces last year, in the aftermath of then-army chief Abdel Fattah al-Sisi's ouster of elected Islamist President Mohamed Morsi.

Human Rights Watch is one of a number of international and Egyptian rights groups that have expressed alarm at a severe and increasingly broad crackdown on dissent by authorities since the army's overthrow of Morsi in July 2013.

Whitson, the head of the Middle East and North Africa division at Human Rights Watch, tweeted on Monday morning that she had been held for 12 hours before being deported for "security reasons."

Omar Shakir, author and principle researcher of the group's report on the mass killings, confirmed to Reuters that Roth and Whitson had been denied entry after landing in Cairo and being held by authorities since Sunday night. He said Whitson had left the country and Roth would be leaving on a separate flight later in the morning.

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