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JERUSALEM, April 10 (Reuters) - A Hamas militant drove a powerful car bomb into the Tel Aviv area last month but returned to the occupied West Bank without carrying out an attack, Israel's Shin Bet security service said on Tuesday.

Hamas, an Islamist group that heads the Palestinian unity government, declined to comment on the issue.

Hamas last carried out a bombing in Israel in 2004, one of 60 such attacks the group launched since a Palestinian uprising that began in 2000.

The Shin Bet said the militant was a member of a Hamas cell in Qalqilya, a West Bank city near central Israel, and had driven a commercial vehicle laden with about 100 kg (220 lb) of explosives.

"But the attack was not carried out and the vehicle was returned to Qalqilya," the security service said, without elaborating, in a statement faxed to Reuters.

The vehicle later exploded in a "work accident" in Qalqilya, the Shin Bet said, using an Israeli term for a technical malfunction. It did not say if the blast hurt anyone.

The Shin Bet said nineteen members of a Hamas cell in Qalqilya suspected of involvement in the planned bombing, timed for the Jewish Passover holiday, were seized by Israeli security forces. Their names were not released.

"Terror continues to spearhead the Hamas agenda and serves as a cornerstone of the new Palestinian government," said David Baker, an official in Israeli Prime Minister Ehud Olmert's office.

Hamas established a Palestinian unity government with the secular Fatah faction last month but has not met demands by a Quartet of Middle East mediators to recognise Israel, renounce violence and accept past interim peace deals.

Israeli media reported that investigations continued into why the attack was not carried out inside Israel, with Israeli authorities questioning the suspected Hamas cell.

The Shin Bet said the would-be suicide bomber was able to enter Israel through military checkpoints because he carried an Israeli identity card on the basis of his father's marriage to an Israeli Arab. (Additional reporting by Jonathan Saul in Jerusalem and Nidal al-Mughrabi in Gaza)

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