JERUSALEM — Archbishop Desmond Tutu is planning to enter Gaza today to conduct a U.N. investigation into the killing of 19 Palestinian Arabs by Israeli shells.

After 18 months of being denied a visa by Israel, the Nobel Peace Prize winner is expected to cross the border at Rafah via Egypt.

The archbishop is intending to visit the scene of the incident, in which Israeli forces fired an artillery barrage into the Gazan town of Beit Hanoun early one morning in November 2006.

The first shell hit a house, causing members of the Athamneh family to run out into an alley, where they were cut down by further shells. Almost all the dead were from the same family, the youngest an 8-month-old girl.

The Israeli army carried out its own investigation but found earlier this year that the incident was an accident, and held no individual to account for the deaths. Palestinian Arab human rights campaigners were incensed by the finding.

Mr. Tutu’s trip represents a major showdown between the Jewish state and the U.N. Human Rights Council, which commissioned his inquiry weeks after the incident.

The Israeli authorities gave no explanation for the visa delays but it is known Israel has problems with the human rights council because of its constant focus on the Israeli-Palestinian conflict. Israeli government sources have said the council is politicized and biased for ignoring other human rights violations such as Darfur, while repeatedly censuring Israel.