The Gaza Strip man who blew himself up at a Jerusalem bus stop was one of several Palestinian policemen being probed for suspected involvement with Islamic militants, a Palestinian official said Monday.

Twelve people including a U.S. citizen were injured in the blast Sunday near the main entrance to the city. The bomb was set off by Ayman Radi, 25, of Khan Yunis, seconds after a bus filled with Israeli army soldiers pulled away.The bombing was claimed by Hamas, an Islamic fundamentalist group that has carried out numerous attacks on Israelis in its bid to destroy the September 1993 accord between Israel and the Palestine Liberation Organization.

Radi joined Palestinian traffic police in August as a volunteer, said Marwan Kanafani, a spokesman for PLO leader Yasser Arafat's autonomy government in Gaza.

Hamas sources said Radi joined their group because he felt guilty about helping to put down riots in Gaza City last month in which 15 Palestinian worshipers died.

Israeli newspapers said Radi was a known Hamas sympathizer during Israel's occupation of Gaza, which ended in May, and that he was once shot in the legs during a protest against Israeli soldiers.

Kanafani told reporters that before the attack, "the man was on the list to be questioned by the Palestinian security forces." Radi failed to show up for questioning when he was summoned Dec. 20, Kanafani said.

Several other Palestinian policemen were also being probed for suspected activity with Islamic militant groups, he said. He said he did not know whether the Palestinian Authority was planning to make any arrests in connection with Sunday's bombing.

Kanafani said the Palestinian authority will make sure that the Palestinian policemen will be "neutral" and not affiliated with other groups.

Previously, applicants were asked to disclose their affiliation with any of the Palestinian factions, though membership in Islamic militant groups was not necessarily a disqualifying factor.

Hamas sources say at least 650 supporters of the group have joined the Palestinian security forces.

In a leaflet issued Sunday, Hamas said the bombing was also in retaliation for a Dec. 21 car bombing in an Islamic neighborhood in Beirut, Lebanon, that killed four people.

Among the victims was Fuad Mughniyeh, the brother of Imad Mughniyeh, security chief for Hezbollah, the Iranian-backed Islamic group fighting Israeli soldiers in southern Lebanon. Mughniyeh is accused of masterminding the kidnappings of Western hostages in Beirut in the 1980s.

Israel has declined comment on Lebanese allegations that Israel was behind the bombing.