Police are deployed on key thoroughfares in the capital, which until this week had been spared the violent unrest erupting in provincial towns.

Stores around the capital are shuttered.

The Interior Ministry building and a municipal services building were among targets of protesters’ anger Thursday.

Police have repeatedly shot at protesters in more than three weeks of violence that has rocked this country. Officials tally at least 23 dead, including four killed overnight.

The unprecedented violence has revealed deep anger against autocratic President Zine El Abidine Ben Ali’s government.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP’s earlier story is below.

TUNIS, Tunisia (AP) — Police opened fire and killed four people overnight in Tunisia, opposition members said Thursday, as youths angry about unemployment defied a government curfew aimed at calming more than three weeks of violent protest.

The unprecedented violence has revealed deep anger against autocratic President Zine El Abidine Ben Ali’s government, with rock-throwing youths hitting central Tunis on Wednesday and the army deploying armored vehicles to the capital. Protesters took on police and looters ravaged stores in several working-class areas overnight as gunfire echoed for (kilometers) miles.

The government’s death toll stands at 23, while opposition figures and witnesses say it is more than 50, including the deaths overnight near Tunis and in the northern region of Bizerte. A French and a Swiss citizen were among those killed, the two European governments said Thursday.

Looters raided a supermarket, pharmacy, clothing shops and a bookstore amid overnight chaos, said union leader and human rights advocate Souad Ghousami, a member of the opposition PDP party. Security forces appeared unable or unwilling to intervene, and the military appeared to focus its efforts on public buildings, she said. Many youths were taken into custody.

Despite the appearance of a return to normal life in central Tunis, plainclothes police combed a downtown avenue and about 10 soldiers backed by an army truck guarded the state external communications office — where barbed wire was put up as a precaution amid reports that bands of youths were roving in the capital.

Police have repeatedly opened fire on protesters. The European Union has complained about the disproportionate use of force in a country that has had little history of unrest and is considered an oasis of calm compared to its neighbors, Algeria and Libya.

Ben Ali has gone on national TV in an appeal for calm and to pledge job creation, but his efforts have not done much to stop the unrest.

Mourad Yacoubi, an academic and member of the PDP party, said two people were shot to death and another was severely injured after being hit by gunfire in the Al Intilaka housing project outside Tunis.

To the north, in the town of Menzel-Bourguiba in Bizerte, a young man, Khaled Ben Abderrahmane Mathlouthi, was also killed, said Ghousami.

Ghousami said another person, Skander Khlifi, was shot and killed in the nearby town of Sekma, where two others were also rushed to the hospital with injuries to the stomach and shoulder.

The official death toll has stood at 23 for several days. Amid complaints about a lack of openness, the government opened a media hotline, but calls to the line went unanswered on Thursday.

The Swiss Foreign Ministry said Thursday a woman with dual Swiss-Tunisian citizenship died in unrest in northern Tunisia. Swiss radio reported the woman was killed by a stray bullet while watching a protest a day earlier.

Another victim was a professor of computer science in France, at the University of Technology at Compiegne. University spokeswoman Nadine Luft said Hatem Bettahar had taught there for a decade and had traveled to Tunisia for vacation to see his mother.

Slah Nebti, a Tunisian teacher, said Bettahar was shot to death Wednesday by police in a protest in the central city of Douz. He filmed a video of the shooting’s aftermath and posted it to Facebook: It showed Bettahar lying in a pool of blood, and the crowd shouting "God is Great!" in Arabic.

The French Foreign Ministry said it was looking into the circumstances of Bettahar’s death.

Ben Ali, 74, has maintained an iron grip on Tunisia since grabbing power 23 years ago in a bloodless coup, repressing any challenge to a government many see as corrupt and intolerant.

The image of stability and religious moderation helps draw millions of mostly European visitors a year to the Mediterranean beaches of this small North African nation, making tourism the mainstay of the economy. The economy’s weak point is unemployment — officially nearly 14 percent, but higher for educated youths.

But Ben Ali’s tight control also has created the simmering sense of anger and resentment that erupted in the capital and outside it. He has locked up many opposition figures, clamped down on dissent and kept tight control over the media.

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Associated Press writer Elaine Ganley contributed to this report.