Cairo, Egypt ? An explosion apparently set off by a bomber on a motorcycle hit a tour group shopping in a historic bazaar Thursday, killing at least two people and wounding 18 — the first attack targeting foreign tourists in the Egyptian capital in more than seven years.

The dead included a French woman. Four Americans were among the 18 wounded, the Interior Ministry said. Brig. Gen. Nabil al-Azabi, head of security in Cairo, said the second person killed might have been the bomber.

Many of the wounded had severe injuries from nails packed in the bomb, doctors said. The U.S. Embassy in Cairo warned Americans to stay away from Khan al-Khalili, the sprawling bazaar area, and to use prudence elsewhere in the city, said embassy spokesman James L. Bullock. He would not confirm American casualties.

Egypt has seen a long period of calm since it suppressed Islamic militants who in the 1990s carried out bombings and shootings against tourists in their campaign to bring down the government. The last significant attack on tourists in Cairo was in 1997.

At least two witnesses said a man on a motorcycle appeared to have set off a bomb near a tour group in the al-Moski bazaar. Al-Azabi said initial investigations suggested the explosive was a homemade nail-packed bomb that went off prematurely.