In his highly-anticipated address, Donald Trump called on Muslim leaders to do their share to fight "Islamist extremism".
His speech put much of the burden on the region to combat militant groups, while urging unity among religions.
Jordan's King Abdullah says it's a vital message that everyone, everywhere must understand.
"Terrorist groups do not inhabit the fringes of Islam, they are altogether outside of Islam. They are khawarij, outlaws of Islam. And Arabs and Muslims make up, as you pointed out sir, the majority of their victims. Intolerance and ignorance will only aid terror groups."
King Abdullah also said a "just and final settlement" of the Israeli-Palestinian conflict is necessary for combating terror.
Egyptian President Abdel Fattah El-Sisi says there's no shortcut in the repair of the operations in the dangerous face of terrorism.
"We must face the various terrorist organisations in a comprehensive and synchronised way, on all fronts. And in this context, you all understand that Egypt daily faces a lesson in a war against terrorists in the West of Sinai, in which we continue to win and make advances, with care and scope in order to eradicate terrorism, with as little losses as possible and preserving the lives of civilians of our great country."
Indonesia's President, Joko Widodo, called on fellow Muslims.
"Muslims, all over the world, should unite. Unite to enhance Islamic brotherhood. The unity of Muslim is the key to success of combating terrorism."
Mr Trump also called on Muslim nations to isolate Iran, saying the Iranian government funds terrorism and describing its involvement in the Syrian civil war as "destabilising".
Malaysia's Prime Minister Najib Razak says it's not only for the sake of regional stability, but also for the unity of what is known as the Umma, the global community of Muslims bound together by ties of religion.
"I am aware that there is a widespread belief here that Iran has contributed largely to the instability in the region. As a country that enjoys and values good relations with countries and regions Malaysia feels that Iran must avoid, and should avoid, any action that could be seen as interfering in the internal affairs of its neighbours."
Fawzi Barhoum is the spokesman for the Palestinian group, Hamas, which controls the Gaza Strip.
He has rejected Mr Trump's linking of Hamas to terrorism and called on him to look at the situation more broadly.
"US President Trump's statement concerning Hamas movement and describing it as a terror group is altering facts and it is rejected. Terrorism is the terrorism of the Israeli occupation that commits massacres and daily crimes, in addition to their crime against humanity through their siege on the Gaza Strip and their mass murder in the West Bank and Jerusalem. Therefore, this is a complete bias towards the Israeli occupation and confirms the wrong US political approach towards the Palestinian people and their legitimate resistance."
And back in the United States, former Republican Senator Rick Santorum has told CNN he thought the speech was aimed at quite a different audience.
"Not to the Muslim world, not to the leaders there, but to judges in this country (US) who are looking at his immigration ban. It's going to be very hard now to say, oh, this is a Muslim-hater, he hates Islam, you know, he wants to ban Muslims. All the solicitor has to do now is play parts of that speech."
Mr Trump's address was the centrepiece of his visit to Riyadh, which is the first leg of an eight-day foreign tour.
