Egyptian authorities are investigating whether a homicide bomber carried out an attack that killed three people, including an American tourist, in a packed Cairo (search) market, officials said Saturday.

The rudimentary 7-pound bomb packed with nails exploded Thursday in Khan al-Khalili (search) tourist bazaar, killing an American, a French woman and an unidentified third person, who investigators have said probably was a homicide bomber.

Egyptian Prosecutor General Maher Abdel Wahed (search) on Saturday increased the number of injured by one to 19. Three injured American tourists were in stable condition, said Tourism Ministry spokeswoman Hala al-Khatib. A Frenchman remained in critical condition.

Abdel Wahed also said investigations believed the attack was "an individual act."

In a briefing to Cabinet (search) ministers, Egypt's interior minister suggested a man carrying an explosive was responsible for the blast, government spokesman Magdy Rady said.

"It is either a suicide bombing or it exploded on him prematurely," Rady said.

Rady said if it was a homicide bombing, it would be the first such attack carried out in Egypt, a country that suffered Islamic militant attacks on foreigners during the 1990s aimed at overthrowing the secular regime of President Hosni Mubarak.

A Michigan newspaper, citing a family friend, identified the American killed as Alex Mirandette, 18, from the Grand Rapids suburb of Kentwood.

The victim's identity could not be confirmed and U.S. Embassy officials in Egypt declined to give details on the American victims.

The Grand Rapids Press interviewed Julie TenHaaf, a sister of Michiel Kiel, 21, who was among three other Americans injured in the Cairo attack. Mirandette's brother, Erik, 22, and another friend, Kristopher Ross, 22, also were wounded.

TenHaaf told the newspaper her brother had finished serving four years in the U.S. Army in Qatar before joining up with his three friends, the Mirandettes and Ross, who had been on a motorcycle tour of Africa before arriving in Egypt.

An Egyptian investigator, speaking on condition of anonymity, said the severe damage to the third victim's torso increased suspicions the blast was caused by a homicide attacker. Police are still looking for that victim's hands to check for fingerprints and are running DNA tests on his remains.

The official said the bomber was carrying the device in a leather bag.

Al-Arabiya satellite TV station aired footage taken by mobile telephone of the scene in the crowded al-Moski bazaar following the blast, showing several bodies lying on the ground.

Investigators, speaking on condition of anonymity, said jailed militants from groups responsible for the violent campaign against the government during the 1990s denied any link to the attack.

A previously unknown group, the al-Ezz Islamic Brigades, claimed responsibility for the attack in an Internet statement, saying it was a message to Mubarak that Islamic militancy still exists in the country. The authenticity of the claim could not be verified.

Egyptian officials sought to limit damage to Egypt's vital tourism industry, stressing there was no evidence so far the bomber was part of a wider group.

Loads of tourists returned to the popular market area in Cairo's old city, but security was heavier than normal.

The attack came as Egypt prepared for the country's first-ever multi-candidate presidential elections later this year.

Opposition and pro-reform groups — which have been holding street demonstrations demanding more comprehensive reforms and the lifting of emergency laws — warned against exploiting the attack to reverse the reform process.

Rady dismissed the worries, saying the political reform debate would not be jeopardized by the attack. On the contrary, he said, "it will bring people together."

The last major burst of violence in Cairo was in 1997, when gunmen attacked a bus of German tourists, killing 11, several months before massacring tourists at a pharaonic temple in the southern city of Luxor in a shooting that left 64 dead, including the six gunmen.