The arrests were in connection to dozens of Facebook pages set up by Brotherhood supporters, urging protests against the military-backed government and denouncing the police, some of them set up the past two weeks.
Social media and Facebook in particular were main platform for organizing the country's 2011 uprising that led to the ouster of longtime president Hosni Mubarak. Since then, fiercely anti-police pages have arisen during years of turmoil by youth of various stripes, including riotous soccer fans who often clash with police.
Of the Facebook pages investigated, at least one had pictures of an individual military officer whom the page said is "under the microscope." Another had a posting calling for the burning of police stations.
Egyptian authorities have arrested thousands of members of the Brotherhood and killed hundreds of its members in clashes with protesters since army chief Abdul-Fattah el-Sissi toppled President Mohammed Morsi, who hailed from the group, on July 3 following giant rallies against Morsi.
The Brotherhood has held non-stop protests demanding Morsi's reinstatement and denouncing the interim government installed by the military after his ouster.
At the same time, Islamic militants based in the Sinai have claimed responsibility for a wave of bombings and shootings targeting police. The government says the Brotherhood orchestrated the attacks, branding it officially as a terrorist organization, but the group denies that claim.
The new arrests, which took place Wednesday and Thursday, were the first to target a group said to be administering Facebook pages.
In a statement, the Interior Ministry accused the detainees of using the networking site to "incite violence, target citizens, make bombs and carry threatening messages." It said one called for the formation of an Islamic army and two others circulated names and pictures of police officers.
Among those detained was a teacher from the Nile Delta city of Damanhour, who allegedly posted on his Facebook page a "statement inciting the burning of police vehicles," the ministry said.
Two others, a government employee and his son, were arrested for running a page called "Revolutionaries of Beni Suef," a southern province. The page, set up on Jan. 21, has around 500 followers.
One of its postings shows three pictures of an army officer with his children. A caption with the post identifies him as part of the "el-Sissi militia."
"I say to all el-Sissi dogs, everywhere, you are under the microscope," it read.
Six others detained in the city of Damanhour for running Facebook page called "Damanhour Ghosts." The page mostly carries criticisms of the military and government and calls for the freeing of detainees - though one picture shows the country's top leaders, including el-Sissi, in red prison uniforms with nooses dangling above them.
Others were arrested in connection to a page called "Anti-Coup Hooligans Brigade," launched in October, which includes pictures of policemen the page accuses of killing protesters, pictures of youth throwing firebombs and instructions on how to make paint-filled eggs to throw at the windshields of police vehicles.
The ministry said several among the 11 were arrested for sharing postings from other pages called the Free Islamic Army.
Security officials say that since the crushing of two pro-Morsi protest camps in August last year, Brotherhood pages posted names, pictures and personal details about police officers they accuse of involvement in the assault. The day witnessed one of Egypt's worst bloodbaths, with hundreds killed.
The postings led Interior Ministry to issue a warning to its officers to change mobile phones, addresses and wear civilian clothes.
Over the past months, several drive-by shootings by militants targeted senior police officers including Lt. Col. Mohammed Mabrouk, whom authorities say was involved in investigating Muslim Brotherhood leaders.
Authorities also expanded the crackdown to go after the Qatar-based Al-Jazeera TV news network, which they have long accused of bias in favor of the Brotherhood. The network denies any bias.
On Wednesday, 20 Al-Jazeera journalists were ordered put on trial on charges of aiding or joining a terrorist group and endangering national security.
The charges now effectively depict the station's reporting as support for terrorism after the government declared the Brotherhood a terror organization in December.
After Wednesday's indictment of the 20, State Department spokeswoman Jen Psaki said Washington was "deeply concerned" about the lack of freedoms in Egypt and the country's "egregious disregard for the protection of basic rights and freedoms."
Egypt's Foreign Ministry spokesman, Badr Abdelattie, rejected the U.S. criticism on Thursday, insisting that the judicial system ensures fair trials and the government does not interfere in its work.
No date has been set for the trial and the full lists of charges and defendants have not been released.
The 20 defendants are known to include three men working for Al-Jazeera English: Acting bureau chief Mohammed Fahmy, a Canadian-Egyptian, award-winning correspondent Peter Greste of Australia and producer Baher Mohamed, an Egyptian. The three were arrested on Dec. 29 in a raid on the hotel suites where they were working.
Greste's parents, Lois and Juris, called the arrests of the three an abuse of human rights, free speech and journalists' freedom to report.
"Someone didn't like their report. For that, they are now put into a maximum security prison for what is clearly punishment - not mere detention," Juris Greste told reporters in Brisbane. "This is most undeserved, outrageous and shameful."