(Adds details, Italian PM comments)

By Stephen Brown

ROME, April 24 (Reuters) - Palestinian President Mahmoud Abbas said on Tuesday a violation of a five-month ceasefire by Hamas was an exception and would not be repeated.

Abbas also said Israel should show restraint to avoid a security deterioration.

"The violation of the truce is an exceptional event that will not last," Abbas told news conference with Italian Prime Minister Romano Prodi in Rome.

Hamas's armed wing said it fired rockets at Israel from the Gaza Strip in response to an Israeli strike at the weekend that killed nine Palestinians.

"We agreed this truce because you can't talk with the noise of cannons. If violations happen, we have to work very hard to return the situation to normal quickly," said Abbas.

His secular Fatah formed a unity government with the Islamist Hamas last month in a bid to end fighting between the Palestinian groups.

There was no immediate Israeli government comment on the rocket fire, which caused minor damage but no casualties. The Jewish state was celebrating its Independence Day.

Israeli Prime Minister Ehud Olmert was to meet security advisers on Wednesday but one newspaper said any Israeli military response would be limited.

"I take this opportunity to appeal to Israel to show the necessary self-control so that this will not happen again," said Abbas, who met Pope Benedict in the Vatican earlier on Tuesday.

Prodi said while he was optimistic about the Middle East peace process in general, and especially what he called growing diplomatic involvement by Arab states including Saudi Arabia, he was concerned about the truce violation by Hamas.

"I condemn it firmly and hope it is only temporary," said Prodi, whose centre-left government has expressed support for the new unity leadership of the Palestinians.

Prodi made an appeal for the release of missing BBC journalist Alan Johnston, who was kidnapped in the Gaza Strip last month.

Abbas was asked by reporters about the fate of captured Israeli soldier Gilad Shalit, abducted by Hamas and two other Palestinian militant groups in a cross-border raid from Gaza last June.

"As far as we know he is alive and in good health," said Abbas.

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