Egypt's military-backed interim government has declared two Cairo vigils by backers of ousted President Mohamed Morsi "unacceptable threats" to national security.
Authorities ordered police to put an end to the sit-ins, but to stay within the law and the constitution.
Morsi's Muslim Brotherhood movement says it fears the military may be setting up the demonstrators for what it says would be another massacre. Security forces shot at demonstrators in Cairo Saturday, killing at least 80 people.
Protesters are holding vigils outside a large mosque in eastern Cairo and the city's main university campus.
The human rights group Amnesty International says the military-backed government's order to clear out the vigils gives forces the "seal of approval" for further abuse.
Nearly 200 people have been killed in violence since the Egyptian military removed Morsi from power on July 3. Many of the victims had been supporters of the former president.
In addition to overthrowing Morsi, the army suspended Egypt's Islamist-drafted constitution, following massive protests against his rule.
The country's interim government plans to hold a referendum within five months to ratify amendments to the constitution, with parliamentary elections taking place early next year, followed by a new presidential election.
U.S. President Barack Obama Tuesday asked two senior Republican lawmakers - Senator Lindsey Graham and fellow Republican Senator John McCain - to travel to Egypt next week to meet with military leaders and the opposition.
Egypt's crisis has triggered questions about continuation of the $1.5 billion in annual U.S. military and economic aid to Egypt. Last week, the Obama administration said it will not declare the overthrow of Morsi as a coup, thus allowing the U.S. to continue providing the financial aid.
An attempt by U.S. Sen. Rand Paul to cut Egyptian aid failed Wednesday when senators voted by a large margin [86-13] to postpone indefinitely any consideration of the measure.