CAIRO (Reuters) - A U.S. think tank analyst and former diplomat who has written articles critical of Egypt's government was blocked from entering the country to attend a conference on Saturday.

Michele Dunne, a former diplomat once posted to Cairo and a senior associate at the Washington, D.C.-based Carnegie Endowment for International Peace, said she was given no reason when she was turned back at Cairo International Airport.

"I come into the country two to four times a year, for the past 10 years at least," Dunne told Reuters from Frankfurt's airport, where she was waiting for a flight to return to the United States on Saturday after leaving Cairo that morning.

A foreign ministry spokesperson declined to comment and referred questions to the interior ministry. Calls to the ministry and its spokesperson were not answered.

Dunne, who served in the U.S. foreign service for 17 years, including a posting at the U.S. embassy in Cairo, was coming to Egypt for a conference of the Egyptian Council for Foreign Affairs, she said.

"I write about Egypt frequently ... I don’t think there's been anything really different on my part. It seems to me the change is more on the Egyptian side. It seems the tolerance for any kind of writing that is critical is much less than it was before," Dunne said.

Dunne authored an article published Dec 2 that highlighted the challenges facing human rights organizations in Egypt and other Arab countries.

Under President Abdel Fattah el-Sisi, the former army chief who ousted elected Islamist President Mohamed Mursi last summer, Egypt's government has pushed non-governmental organizations (NGOs) to register under a Hosni Mubarak-era law.

Human rights groups say the push to enforce the old law aims to restrict their activities and funding, raising concerns that Sisi's government is rolling back freedoms won in the 2011 uprising that ousted Mubarak.