By the BBC's Frank Gardner

As US Defence Secretary Donald Rumsfeld flew towards Saudi Arabia, his trip was already being overshadowed by fresh violence in the Middle East.

The killing of Israeli settlers by Palestinians, and the subsequent Israeli attack on Gaza, could not have come at a more awkward time for the US administration.

Arab concerns

Restrain Israel Define 'terrorism' Limit Muslim casualties Provide proof of Bin Laden's guilt Maintain low profile for western military action in Gulf

Mr Rumsfeld's visit to Riyadh is the first leg of a four-nation tour to shore up support for America's war on terrorism.

He is also expected to visit Egypt, Oman and Uzbekistan.

President George W Bush badly needs the support of the Arab and Muslim world in his war against global terror.

He had been hoping to keep the Israeli Palestinian conflict out of the news while he concentrated on building up an international coalition.

Broad support

Now, Israel's attack on the Palestinian city of Gaza is bound to intrude on Mr Rumsfeld's discussions with Arab leaders.

Arab governments have broadly supported America's war on terror, but they have conditions of their own.

They want the word terrorism clearly defined.

Donald Rumsfeld wants to reassure Muslim countries

Earlier this week, the 22-member Arab League called the Palestinians victims of modern terrorism.

Arab leaders will be urging Mr Rumsfeld to restrain Israel or risk losing the support of the Arab world.

Over the next few days, he will hear other concerns too from the leaders of Saudi Arabia, Egypt and Oman.

They are all playing host to western forces, a fact that could prove embarrassing if any western military action in Afghanistan leads to Muslim casualties.

Arab leaders will urge Mr Rumsfeld to keep those casualties to a minimum.

They would also like to be shown some proof that links Osama Bin Laden or the Taleban to the attacks on the US on 11 September.

Until that proof is provided, there is a deepening suspicion among many ordinary Arabs that their region is being dragged into a military campaign that they do not support.