Cairo ? A homemade bomb exploded in a 650-year-old bazaar packed with tourists Sunday, killing a French woman and wounding at least 21 people, most of them foreigners.

Within an hour, police found a second bomb and detonated it safely. Security officials said three people were in custody.

An expert on Islamic extremism said the attack might have been a response to Israel’s deadly offensive in Gaza last month.

Tourism is one of Egypt’s major sources of foreign income and has been a target in past attempts to harm the government, which is now trying to negotiate a long-term Gaza cease-fire. Sunday’s attack was the first on tourists in three years.