A bomb exploded Wednesday afternoon near one of the largest checkpoints between Jerusalem and the West Bank, killing two Palestinians and injuring 16, including six Israeli border patrol officers, according to Palestinian and Israeli medical officials.

The blast occurred as Israeli police and border patrol officers were tightening security at Jerusalem checkpoints after receiving reports that an attacker might be trying to enter Jerusalem from the Ramallah area in the West Bank, according to Gil Kleiman, a spokesman for the Israeli national police.

Kleiman said the explosion occurred just as several border patrol officers were stepping from their vehicle to investigate a car parked about 200 yards from the busy Qalandiya checkpoint on the northern edge of Jerusalem.

"It was a medium-sized bomb that we suspect was planted in a bag placed on the ground near the road," Kleiman said. He said police believe that an attacker intended to bring the bomb into Jerusalem, "saw the policemen, dropped the bag and left the scene."

He said police suspect the bomb may have been detonated by remote control. The blast spewed shrapnel for dozens of feet, spraying the border patrolmen, Palestinian pedestrians and a bus driver with shards of metal and igniting two cars.

Salah Abu Sneinah, 60, was killed and a 6-year-old Palestinian boy remained in a coma late Wednesday in Ramallah, according to Palestinian medical officials. Two of the six injured border patrolmen were being treated for severe head wounds, Israeli hospital officials said.

"I saw a border policeman talking to some people, and then suddenly there was a strong explosion," said Zaki Salayme, 33, a Palestinian resident of East Jerusalem who was driving a minibus from the Damascus Gate in Jerusalem's Old City to the checkpoint. "I flew out of my seat and the bus jumped back. I saw a soldier fly, and I saw another person also fly."

A piece of shrapnel was embedded in Salayme's chin and blood was smeared on his shirt as he awaited treatment at Jerusalem's Hadassah Ein Karem Hospital.

Al-Aqsa Martyrs Brigades, the militant wing of Palestinian leader Yasser Arafat's Fatah movement, asserted responsibility in calls to local offices of international news agencies. "This is a response and reaction to the occupation's crimes in the West Bank and Gaza Strip," a caller told the Reuters news agency. "There will be more attacks."

The explosion was the first bomb attack in a month. A bomb planted near a Tel Aviv bus station killed an Israeli soldier and wounded 30 people on July 11. As Israeli security operations have made it increasingly difficult for Palestinian attackers to enter Israel, militants have focused their attacks on crossings.

Meanwhile, in the southern Gaza Strip, Israeli forces fired missiles at a neighborhood in the city of Khan Younis, injuring 12 Palestinians, according to news service reports. Israeli officials said the missiles were aimed at an open area in an effort to deter gunmen. They also said 13 Palestinian houses and apartment buildings were leveled.

Special correspondents Samuel Sockol and Sufian Taha contributed to this report.