Israel has blocked a UN fact-finding mission to the Gaza Strip that was to be led by South African Nobel laureate Desmond Tutu, the UN says.

Mr Tutu's team would have investigated last month's killings of 19 civilians in an Israeli artillery barrage in the northern town of Beit Hanoun.

But Israel had not granted the former Archbishop of Cape Town the necessary travel clearance, a UN official said.

The Israeli government said it had not formally denied visas to the UN team.

Mr Tutu's team was supposed to report its findings to the Geneva-based UN Human Rights Council by Friday.

Spokeswoman Sonia Bakar said Mr Tutu had other engagements and could not wait any longer for Israeli permission to travel.

"It has been cancelled. We were supposed to go yesterday (Sunday)," she said.

An Israeli government spokesman said it had not made a final decision on whether to grant visas for Mr Tutu's team.

He said the government did "not have a problem not with the personalities, we had a problem with the institution. We saw a situation whereby the human rights mechanism of the UN was being cynically exploited to advance an anti-Israel agenda".

Shelling 'an accident'

The 47-nation Human Rights Council authorised the mission last month after condemning the killings.

It asked Mr Tutu to assess the situation of victims, address the needs of survivors and make recommendations on ways to protect Palestinian civilians against further Israeli attacks.

The shelling, which Israel said was unintended, came after its troops wound up a week-long incursion designed to curb Palestinian rocket attacks on Israel from the town.

The Israeli army claimed Beit Hanoun was a rocket-launching stronghold.

Mr Tutu - the winner of the 1984 Nobel Peace Prize for his fight against apartheid in South Africa - chaired the country's Truth and Reconciliation Commission after the end of white minority rule.