Three bombs have rocked the Egyptian resort town of Dahab, killing at least 22 people.
More than 150 are reported to be wounded, but casualty figures are still far from clear.
The Interior Ministry says some foreigners are among the dead, but most of the casualties appear to be Egyptian.
Three bombs exploded in the market area of the Red Sea resort of Dahab not long after dark, when the area would have been packed with vacationers.
Cairo resident Farid Tadros is staying in a dive camp a few hundred meters from the blast sites.
Mr. Tadros said, "I didn't feel them but they were definitely very, very loud. They had the exact same sound to them, which was kind of concerning. Some people said they saw smoke. I didn't see any smoke from where I was."
Tadros said the bombs went off in the heart of the tiny resort town, where most of the restaurants are.
The Interior Ministry said a restaurant, a cafe and a supermarket appeared to be the targets.
In a statement carried on the state news agency, Egyptian President Hosni Mubarak called the attacks a "wicked terrorist act" and vowed to track down those responsible.
Egyptian vacationer Basma Adnan is staying in a nearby hotel and told Egyptian state television that she heard the blasts.
She says, "It was frightening. There are ambulances outside. They have closed the hotel on us. They are stopping anyone from going out or coming in, and everyone is being searched."
Police say they have sealed off the entire area on the eastern shore of the Sinai peninsula.
Many of the wounded were taken to the Dahab hospital, but the provincial governor says some have been taken to Sharm el-Sheikh.
A medical crew was also reported to be leaving Cairo by helicopter to evacuate some of the most serious casualties.
The Dahab attacks come a day after the broadcast of a new audiotape by al-Qaida leader Osama bin Laden, who warned that he considers Western civilians to be legitimate targets, accusing them of complicity with their governments in what he called a "Crusader-Zionist war" against Islam.
The Sinai Peninsula has been hit by a series of deadly terrorist attacks over the last few years.
Multiple bombings in Sharm el-Sheikh killed more than 70 people last July. In 2004, at least 34 died in bombings around Taba, on the Israeli border.
Dahab is a resort popular with foreign tourists and backpackers, who come for the spectacular scuba diving and snorkeling available nearby.
But the attacks came in the middle of an Egyptian holiday, when Dahab hotels would also have been packed with Egyptians taking advantage of the long weekend.
Egyptian Coptic Christians marked the Easter holiday on Monday, and Tuesday is known as Sinai Liberation Day, marking the return of the Sinai Peninsula to Egyptian control after the 1973 war with Israel.
The long weekend also marks the traditional beginning of spring in Egypt.
Sinai resorts are popular with Israeli tourists, but Israeli sources say the Passover holiday probably meant that few Israelis were in Dahab at the time of the attacks.