NETANYA, Israel ? A Palestinian suicide bomber blew himself up Sunday near the unguarded entrance to a crowded cafe in this seaside city, injuring more than 50 people. But police said the sight of an Israeli soldier emerging from the cafe apparently deterred the bomber from entering, averting a larger catastrophe.

The militant group Islamic Jihad claimed responsibility for the attack and called it a “gift to the heroic people of Iraq.” The blast — the first suicide attack inside Israel since the start of the U.S.-led war in Iraq, and the first since a bus bombing in the northern city of Haifa killed 17 people 3 1/2 weeks ago — shattered windows, overturned outdoor tables and sent shrapnel flying in all directions, witnesses said.

“It was a huge explosion,” said 32-year-old Zohar Bat Sharon, who was seated inside the cafe with her husband and 1-year-old son, Maayan. “Pieces of glass and flesh fell into my baby’s carriage — my husband snatched up the baby, and I found myself in the hospital.”

The infant was unhurt; his mother was treated for shock. Hospital officials said 56 people suffered injuries ranging from minor cuts to serious wounds. A soldier who was one of about a dozen troops in the vicinity when the blast hit was reported to be in critical condition with abdominal injuries and a shrapnel wound to the neck.

Witnesses said that just before 1 p.m. the Cafe London, a popular hangout at the center of an open-air mall and promenade in the heart of Netanya, was packed with customers enjoying a sunny Sunday.

District Police Chief Avi Biran said an Israeli soldier in uniform emerged from the cafe just as the bomber approached the entrance.

“Maybe he panicked and so he blew himself up outside,” Biran said. “If he had blown himself up inside, it would have been worse.”

Indoors, the strength of the blast would have been magnified by the confined space, probably causing many more casualties, officials said. Israeli media quoted police sources as saying the bomb was a relatively small one, containing about 6 pounds of explosives but studded with nails and small pieces of metal.

David Baker, an aide to Israeli Prime Minister Ariel Sharon, called the bombing a “brutal reminder of the cruelty of Palestinian terrorism.” The Palestinian Authority, whose new prime minister, Mahmoud Abbas, is expected to form a government in coming weeks and will be under heavy pressure to halt such attacks, also condemned the bombing.

Israel had been on high alert against potential attacks Sunday, a historically volatile day of protest by Palestinian citizens of Israel known as Land Day. It has been an annual observance since 1976, when six Palestinians were killed in a protest against Israeli confiscation of Arab land.

Land Day demonstrations were held in several predominantly Arab towns inside Israel, but the protests were generally peaceful.

Israel also has been on edge since the start of hostilities in Iraq, although fear of a missile attack by Iraqi President Saddam Hussein has diminished since the early days of the fighting.