CAIRO (AP) — Three bearded men approached a university student and his girlfriend during a romantic rendezvous in a park and ordered them to separate because they weren't married, according to security officials. An argument broke out, ending with one of the men fatally stabbing the student.

The June 25 attack has alarmed Egyptians concerned that with an Islamist president in office, vigilante groups are feeling emboldened to enforce strict Islamic mores on the streets.

Islamists, including members of one-time violent groups, were empowered after last year's ouster of Hosni Mubarak's secular regime by a popular uprising. They formed political parties and won about 70 percent of parliament seats in elections held some six months ago, although a court dissolved the legislature.

Moderate Muslims along with liberal and women's groups now worry that Mohammed Morsi's presidency will eradicate what is left of Egypt's secular traditions and change the social fabric of the mainly Muslim nation of 82 million people.

Some activists say Islamists already are flexing their muscles in areas outside Cairo and other main cities, taking advantage of the absence of civil society groups and tenuous security in the areas.

They cite reports of efforts to persuade drivers of communal taxis, mostly minibuses that can seat up to 16, to segregate women and men passengers. In some instances, women's hairdressing salons were told to get rid of male employees or threatened with closure.

"If Islamists are to try and take over the streets and enforce their version of Islam, they will do it in rural areas, at least initially," said Yara Sallam from Nazra, a women's rights group.

The security officials said there was no concrete evidence linking the June 25 killing to radical Islamic groups in Egypt, but it still has stoked fears.

Islamist groups, including Morsi's Muslim Brotherhood and the ultraconservative Salafis, denied any link to the murders.

Rights groups say they have sent teams to investigate the Suez killing and establish whether Islamists were behind the attacks.

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On the same day, two musicians, who were brothers, were murdered as they were traveling home after performing at a wedding in the Nile Delta province of Sharqiyah, officials said. Radical Muslims consider music "haram" or prohibited, as a distraction from religious duties.

Two ultraconservative Salafi Muslims were arrested, but officials said it was not clear if the killings were religiously motivated.

Nonetheless, thousands of residents of Abu Kibeer, the victims' hometown, protested the killings, cutting off roads and disrupting train services by sitting on the rails. They also destroyed the local offices of a charity they suspected the culprits belonged to and torched the home of one suspect.

Some activists believe that the Brotherhood is at least quietly condoning nonviolent activity designed to bring the country more in alignment with Islam's teachings — a founding goal of the 84-year-old fundamentalist movement.

"They may not be involved but they are turning a blind eye to what their low and middle rank members do on the streets," said Nehad Abul-Omsan of the Egyptian Center for Women's Rights.

"What they do is like test balloons for their leaders. If society stands up to what they do, then they know it is not time yet to Islamize. If people accept it, then they ask them to do more. What we need is a clear and public commitment to freedoms by the leaders of Islamic groups."

About 100 activists, political parties and non-governmental groups have issued a statement calling on Morsi to protect women against what it said was growing incidents of harassment, particularly against those not wearing the Muslim veil.

Ahmed Hussein Eid, 20, was attacked while enjoying the evening with his girlfriend in a quiet park that is a favorite spot for romantic rendezvous in Suez, according to the security officials, who gave the account on condition of anonymity because they were not authorized to speak to the media.

The officials did not say what the two were doing when challenged by the three men who arrived at the scene on a motorbike.

But the officials, citing initial testimony of the girlfriend, said the men told the couple they should not be together because they were not married and must immediately leave and go their separate ways. An argument followed and one of the three men stabbed Eid in the upper left thigh, near his genitals. He was hospitalized and died of his wounds on Monday, the officials said.

Suez — a hotbed of the uprising — is a stronghold of Islamists and voted heavily in favor of Morsi in the June 16-17 presidential runoff against Ahmed Shafiq, a career air force officer and the last prime minister to serve under Mubarak. The killing took place one day after Morsi was declared the winner.

Such killings are extremely rare, but activists say Islamists are trying to impose their will on communities outside Cairo.

For example, Islamists in the city of Marsa Matrouh on the Mediterranean are distributing leaflets to patrons of seaside cafes and beaches urging them not to listen to music or watch football on television.

Some concerts at university campuses reportedly have been canceled following threats by Islamists and others have enforced the separation of men and women in classrooms and during out of town excursions.

"A lot of minibuses now play Quranic recitations on their radios instead of loud popular music as it is custom," said Ali Higris, a student from Maasarah, a working-class suburb south of Cairo.

Fully veiled women are also harassing women not wearing a veil or wearing colorful ones while traveling on the women-only train cars of Cairo's busy subway, according to activists monitoring women's rights.

Egypt has for more than 40 years been preoccupied with dealing with the threat posed by radicals seeking to create an Islamic state in the country. Mubarak, backed by the U.S., used that threat to maintain tight control over the country.

Morsi, 60, has not mentioned implementing Islam's Shariah law since he narrowly won the presidential race. That was a departure from his hard-line Islamic rhetoric in the run-up to the first round of voting in May, when the field of 13 candidates included several Islamists, causing many to accuse him of pandering to voters and seeking support from secular political groups in his power struggle with the military.

Many fear the Brotherhood and its allies are closer than ever to realizing the dream of an Islamic government in Egypt and are looking to Morsi to make it happen.

In telling legal cases, a group of police officers has sued the Interior Ministry, which is in charge of security forces, to rescind punitive measures taken against them for growing beards, a hallmark sign of piety. A group of employees from EgyptAir also is taking the state-owned national carrier to court in a bid to lift the ban on growing beards.

"For two years, I have been shaving my beard and apologizing to God because there was a repressive decision against growing it," said police Lt. Ahmed Hamdi. "Why should I be barred from exercising a religious ritual? Now the head of the executive (Morsi) is a bearded man."