RIYADH, Saudi Arabia - Projecting its ambition for regional leadership, Saudi Arabia said Tuesday it has lined up most of the Arab world, NATO member Turkey and several African and Asian countries behind a vaguely defined "Islamic military alliance" against terrorists.

The move allows the kingdom, which follows a deeply conservative interpretation of Islam, to cast itself as a leader in the fight against extremism.

But absent from the alliance are the Shiite-led countries of Iran and Iraq, as well as Syria, whose government is backed by Tehran. And that omission raises questions about whether the 34-member bloc is primarily intended to present a unified front against extremists - or to also serve as a Sunni deterrent to Iran, Saudi Arabia's main regional rival.

Riyadh supports rebels fighting to overthrow Syrian President Bashar al-Assad and has been leading an Arab coalition against Iran-supported Shiite Houthi rebels in Yemen since March. It is also part of the U.S.-led coalition fighting Islamic State militants in Syria and Iraq.

The announcement on state media said the Saudi-led alliance is being established because terrorism "should be fought by all means."

Deputy Crown Prince and Defense Minister Mohammed bin Salman said at a rare news conference that the bloc will develop mechanisms for working with other countries and international bodies to support counterterrorism efforts. Their efforts would not be limited to countering the Islamic State, he added.

When asked if this meant the alliance would also counter Shiite militants, Salman replied that the coalition would fight terrorist groups "regardless of their categorization," particularly in Syria and Iraq, where he said there will be cooperation with the international community.

U.S. Defense Secretary Ash Carter, visiting Incerlik Air Base in Turkey, said: "In general, at least, it appears that it's very much aligned with something that we've been urging for quite some time, which is greater involvement in the campaign to combat ISIL by Sunni Arab countries."