United States presidential candidates Hillary Clinton and Donald Trump have been criticized by human rights groups for meeting with Egyptian President Abdel Fattah el-Sisi on the sidelines of the United Nations Summit for Refugees and Migrants on Monday.

"Mr. Trump expressed to President el-Sisi his strong support for Egypt’s war on terrorism, and how under a Trump Administration, the United States of America will be a loyal friend, not simply an ally, that Egypt can count on in the days and years ahead," according to a statement released by Trump's campaign.

Trump also expressed "high regard for peace-loving Muslims," despite his repeated calls for banning them entry to the U.S.

Democratic presidential hopeful Clinton also met with Sisi, but didn't shy away from addressing these serious concerns. In particular, Clinton brought up the case of Aya Hijazi, a U.S. citizen who was imprisoned two years ago while operating a NGO in Egypt.

"There’s a key difference in their attitudes toward Sisi," Shadi Hamid, a senior fellow with the Project on U.S. Relations with the Islamic World at the Brookings Institution, told ThinkProgress . "There’s nothing to suggest Trump brought up human rights abuses, where Hillary Clinton very clearly did."

"[Sisi’s regime] is not just repressive, it is one of the most repressive regimes in the Middle East, which is saying something," Hamid added.

"Since taking power via a military coup three years ago, President Sisi has overseen not only the complete reversal of Egypt’s nascent democratic transition but also unprecedented human rights abuses," a group of scholars and activists wrote in an open letter, according to Politico .

"It is not in our interest to embrace him but to use our influence to press for beneficial change in Egypt."

The letter argues that Clinton's and Trump's meetings with Sisi would be seen as an endorsement of his actions. "To meet with him is a policy decision, which should await a later date after much study and assessment of U.S. policy toward Egypt."

After he toppled Egypt's first-ever democratically elected, though highly controversial, government through a military coup, rights groups have accused Sisi of heavy-handedly cracking down on dissidents. Many have been jailed, tortured or have simply disappeared, according to reports.

Sisi has held the mantle of securing the country and fighting terrorism. But his targeting of leftist critics, human rights activists and journalists have cast doubt on this.