RIYADH, May 21 (Reuters) US President Donald Trump, struggling to shake a brewing scandal at home, will attempt a reset toay with the Islamic world after frequently attacking Muslims on the campaign trail last year and trying to ban many from the United States. Trump's afternoon speech at an Arab Islamic American Summit (4:20 p.m. local/9:20 a.m. EDT) will include appeals for Muslims to unite against the threat of Islamic militants. A senior administration official said Trump's basic theme in the speech will be to call for unity and say Muslims need to confront radicalism. Whether he would use his signature campaign phrase "radical Islamic terrorism" to describe the threat was unclear. His speech was still being worked on late yesterday, and some advisers were cautioning him against using the term. Saudi Arabia is the first stop on Trump's initial foreign trip, a nine-day journey through the Middle East and Europe. Trump drew the ire of Muslims during his presidential campaign by calling for a ban on them entering the United States. His attempt early in his presidency to ban people from seven Muslim-majority nations has been blocked by the courts. The speech comes as Trump tries to escape the fallout from his May 9 firing of former FBI Director James Comey amid accusations he was trying to stop a federal investigation into his campaign's ties with Russia last year. The New York Times reported Trump called Comey a "nut job" in a meeting with Russian Foreign Minister Sergei Lavrov last week. The Washington Post said the probe had reached into the White House to include a Trump adviser, who was not named. Trump showed little sign of the pressure during a day of diplomacy today during which he was warmly welcomed by Saudi King Salman. At a royal banquet yesterday night, Trump walked into a colorful spectacle: Men in ceremonial dress and carrying swords chanted in unison to beating drums in a courtyard. Trump, clearly enjoying himself, smiled and swayed, even seeming to dance a little at the center of the group. A strong breeze later blew sand through the area. Trump today is to meet leaders of the six-nation Gulf Cooperation Council as part of his effort to counter Iran with a NATO-like Arab force. Trump and the leaders will also establish a center aimed at cracking down on the ability of Islamic militants to spread their message. He will meet individually with the leaders of Bahrain, Qatar, Egypt, Kuwait and Oman. REUTERS AKC 0737