CAIRO, Egypt — An explosion apparently set off by a bomber on a motorcycle hit a tour group shopping in a historic bazaar yesterday, 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 may 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 Bullock. He would not confirm American casualties in the blast.

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.

In September 1997, two gunmen fired on a tour bus outside the Egyptian Museum in central Cairo, killing 10 people — mostly German tourists. Two months later, militants killed 58 tourists and four Egyptians in an attack at a Pharaonic temple in Luxor, southern Egypt.

Last October, explosions hit several hotels in the Sinai Peninsula, including one in the resort of Taba, killing 34 people. Egyptian authorities say that attack was linked to Israeli-Palestinian violence.

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, a maze of narrow alleys with shops selling jewelry, souvenirs and clothes connected to the biggest tourist souk, or market, Khan al-Khalili.

Al-Azabi said initial investigations suggested the explosive was a homemade nail-packed bomb that went off prematurely. He said the second person killed, whose body was severely mutilated, may have been the man carrying the bomb.

The witnesses were not clear whether the man on the motorcycle was a suicide bomber or threw an explosive.

Police said two people were taken in for questioning and police were investigating a motorcycle found nearby with nails scattered around it. Rabab Rifaat, an Egyptian woman who was shopping in a store several yards from the blast, said a large, organized tour group was in the market when the explosion went off.

The Khan is the most famous of a number of closely packed bazaars near al-Azhar, one of the most prestigious Islamic institutions in the Sunni Muslim world.