CAIRO (Reuters) - An Egyptian rights activist said on Tuesday security officials had confiscated his passport and prevented him travelling to Germany where he was due to speak at a parliament roundtable on the human rights situation in Egypt.

The grounding of Mohamed Lotfy, executive director of local NGO the Egyptian Commission for Rights and Freedoms (ECRF), came on the same day that Egyptian President Abdel Fattah al-Sisi was to begin an official visit to Germany.

Sisi is expected to meet with the German president as well as Chancellor Angela Merkel.

Lotfy, a former researcher with Amnesty International, told Reuters a plainclothes officer told him at the airport: "You're not going to travel, you're going back home." When Lotfy asked why, the officer said, "security reasons" and did not elaborate further.

ECRF said in a statement it "deplores such repressive measures taken by the Egyptian state, attempts to close the Egyptian public sphere and isolating Egyptians from the international community".

Authorities have cracked down hard on the Islamist, secular and liberal opposition alike since then-army chief Sisi toppled elected Islamist president Mohamed Mursi in 2013 after mass protests against his rule.

On Tuesday, an Egyptian court postponed issuing a final ruling over a death sentence recommendation for Mursi and other top Muslim Brotherhood leaders.

Egyptian activists say political dissent is being stifled as officials from former autocrat Hosni Mubarak's police state are gradually rehabilitated.

Egypt's government says it is committed to the country's democratic transition.

Bundestag President Norbert Lammert announced last month that he would not meet Sisi when he came to Berlin on Wednesday. In a letter to the Egyptian ambassador, he cited "a systematic crackdown on opposition groups, with mass arrests, long prison sentences and an unbelievable number of death sentences".

Greens party leader Katrin Goering-Eckardt called the barring of Lotfy from travelling a "slap in the face" to the German government.

"If the government rolls out the red carpet for al-Sisi tomorrow, then it is doing so for an autocrat that has stamped on the principles of justice and democracy."

(Additional reporting by Noah Barkin in Berlin; Reporting by Yara Bayoumy; editing by Katharine Houreld)