Egypt's interior minister said Saturday that security authorities have arrested three suspected Al Qaeda-linked militants who were planning to carry out suicide attacks on vital installations and an unspecified foreign embassy.

Mohammed Ibrahim told a news conference that the men had been in contact with Dawood al-Assady, a leader of Al Qaeda in southeast Asian countries such as Pakistan, and that the group was planning to attack government buildings and a foreign embassy. He did not disclose details.

Security officials with knowledge of the case said a Western embassy was the target, but did not have further information. They spoke anonymously because they were not authorized to speak to the media.

The interior minister said authorities seized 10 kilograms (22 pounds) of ammonium nitrate, a key ingredient in homemade explosives. Security officials also discovered statements issued by Al Qaeda in the Islamic Maghreb, the group's arm in North Africa, on one of the men's computers with information on how to make bombs and rockets, and ways of collecting intelligence.

He said the suspects are also believed to have links with the so-called "Nasr City terror cell," which was broken up last year and its members arrested on accusations of plotting attacks against public figures in Egypt.

The interior minister denied that Al Qaeda is active in Egypt, but said the three men were in contact with Al Qaeda militants abroad.

Egypt's security has sharply deteriorated in the past two years, with Islamic militants suspected of being behind cross-border assaults on Israel as well as a bold attack that killed 16 Egyptian soldiers in the northern Sinai Peninsula last year. Ibrahim told reporters that the men were trying to take advantage of the country's situation to "target innocent civilians and attack foreign diplomatic missions."

Ibrahim said one of the three men had received instructions from al-Assady to contact two members of the Nasr City terror cell.

He added that one of the men had received combat training by members of Al Qaeda in Iran and Pakistan and also had connections with members of Al Qaeda in Algeria. The group was additionally accused of having contacts with someone who is in charge of receiving suspected terrorists on the Turkish border, but not further details were given. Turkey has borders with Iraq, Syria and Iran.

The interior minister named the suspects as Amr Mohammed Abu al-Ela Aqida, Mohammed Abdel-Halim Hemaida Saleh and Mohammed Mostafa Mohammed Ibrahim Bayoumi. Two of the men were detained in the northern coastal city of Alexandria, while the third was arrested in Cairo.

Reflecting the deterioration in security, a U.S. citizen was stabbed outside the heavily fortified U.S. Embassy in Cairo on Friday. Christopher Stone, who works at the American University in Cairo and was recently appointed as the U.S.-based director of the CASA program for intensive Arabic language study "is doing well" and will be released from the hospital soon, the university said in a statement Saturday.

The U.S. Embassy said the perpetrator, who was detained, claimed his motivation was to seek revenge over U.S policies in the Middle East. "The (police) investigation, while still ongoing, has established that the perpetrator acted alone, and the incident was not tied to any larger conspiracy," the embassy said in a statement.

Separately, Egypt's top prosecutor ordered Saturday the release of one of the country's most prominent activists only a day after ordering his arrest pending an investigation related to a protest against the country's interior minister.

Police officials and Egypt's state news agency MENA say that prosecutors are referring Ahmed Maher to a misdemeanor court on lesser charges, including disrupting traffic during a protest in March when activists threw underwear at the interior minister's house to oppose a police crackdown on protesters.

It was the latest charge leveled in recent months against activists for insulting an official in President Mohammed Morsi's government.

Maher, the founder of the April 6 Youth Movement that was at the forefront of the 2011 revolt that ousted longtime President Hosni Mubarak, was arrested at Cairo airport Friday as he returned from a trip to the United States.

His April 6 group credits itself with helping Morsi win last year's tight presidential run-offs against a Mubarak-era official that many activists feared would restore the previous regime. The group was established in 2008 during Mubarak's rule to support workers who were planning to strike on April 6.

Maher has since said he regrets his group's support of Morsi and the Brotherhood, and has accused the president of abusing his powers in ways similar to Mubarak.

Right after his detention, Maher was taken to a heavily fortified prison in Cairo where he was supposed to spend four days pending investigations, but ended up spending one night before being released.

The crackdown on activists comes at a time when Egypt is highly polarized and divided over Morsi's rule. Another prominent activist, Ahmed Douma, was arrested earlier this month and is in prison pending an investigation over allegations he insulted the president in a TV interview.

Just hours before Maher was released, Morsi and his Brotherhood party criticized his detention.

One of the president's aides, Pakinam el-Sharqawi, wrote in a statement on Twitter that Egypt cannot forget Maher's "patriotic role" over the years or his group's "revolutionary contribution."

Similarly, Murad Ali, a spokesman for the Brotherhood's political party, wrote on Facebook that while the Islamist group might disagree with some practices of the April 6 Youth Movement, "arresting him in the airport does not fit the charges he's facing."

Maher was among a number of opposition figures who declined to meet with U.S. Secretary of State John Kerry during his visit to Cairo earlier this year, saying that Washington's handling of Egypt's political turmoil and economic problems is "shallow" and in favor of the Brotherhood.