- West welcomes Saudi plan after criticising Riyadh

- Saudi coalition partners voice confusion over the initiative

- Riyadh sees it as a way to share resources in fighting militancy

- Controversy over Saudi interpretation of Islam an issue

Western nations welcomed Saudi Arabia's new Islamic coalition against terrorism, but confusion over its role, even among its own members, may undermine its ambitions of tackling militancy and deflecting international criticism of Riyadh.

"We look forward to learning more about what Saudi Arabia has in mind in terms of this coalition," U.S. Defense Secretary Ash Carter said on Tuesday, a comment that underscored the uncertainty over how Riyadh's new initiative would work.

Comments from several of the countries that signed up to the initiative appeared to reveal a lack of preparation by Riyadh, which approached partners with an invitation to join a coordination centre but then announced a military alliance.

That confused approach to the project may undermine its goal, not only of creating an effective group to fight militancy, but of assuaging Western fears that Muslim countries are indifferent to the threat posed by Islamic State.

In recent weeks, media and politicians in Western countries have complained about what they see as Saudi Arabia's failure to match their own focus on destroying Islamic State militarily or to combat its militant Islamist ideology.

They have painted Saudi Arabia's Wahhabi school of Islam as the ideological wellspring of jihadism and said its decision to wage war in Yemen instead of deploying more force against jihadists shows it does not see that threat as a priority.

Riyadh has always disputed such accusations, pointing to its jailing of Islamic State supporters, its use of top clergy to decry jihadist groups, its participation in air raids in Syria and its work with the U.S. to counter militant funding channels.

"The kingdom of Saudi Arabia has been subject to criticism in Europe, and France in particular, with regard to extremism and Daesh, and I think it is based on not knowing the facts," Foreign Minister Adel al-Jubeir said on Tuesday, using the Arabic name for Islamic State.

Diplomats in Riyadh said the Saudi focus on Yemen instead of Syria arose partly because it regarded its neighbour's civil war as a more immediate threat to its own security and partly because it disagreed with the strategy against Islamic State.

CONFUSION

When Saudi Arabia's Deputy Crown Prince Mohammed bin Salman announced the new group at a sudden midnight press conference, he called it an "Islamic military coalition", a description that appeared to surprise some of the governments involved.

Armanatha Nasir, Foreign Ministry spokesman for Indonesia, the most populous Muslim state, said the Saudi foreign minister had approached Jakarta twice in the past few days to ask it to join a "centre to coordinate against extremism and terrorism".

However, "what Saudi Arabia has announced is a military alliance, ... It is thus important for Indonesia to first have details before deciding to support it," he said. Jakarta had not yet decided whether to join the group.

Chief Security Minister Luhut Pandjaitan said later: "We don't want to join a military alliance."

In a Tuesday meeting with reporters, Jubeir painted the coalition as a grouping that would allow member states to request or offer assistance among themselves in fighting groups they designate as terrorists.

Such assistance could include military force, financial aid, materiel or security expertise, Jubeir said, and would have a permanent base in the Saudi capital Riyadh. However, more detailed specifics of the plan were still under discussion.

Of the 34 countries Riyadh said had signed up for its coalition, several of those contacted by Reuters appeared to have different conceptions of what it would actually entail, while some said they had not been officially notified.

Pakistani Senator Sehar Kamran, who is on the Senate defence committee and lived in Saudi Arabia for many years, said a phone call from Reuters was the first she had heard of the alliance.

"I haven't seen the news yet," she said. Asked if this had been debated in the Senate or National Assembly, she said: "No. Not yet."

The country's Foreign Secretary Aizaz Chaudhry was quoted in the daily newspaper Dawn as saying he had been surprised to read of Islamabad's inclusion and was seeking details from Riyadh.

SECTARIANISM

In Saudi Arabia, the proposal was quickly endorsed by the Council of Senior Scholars, the grouping of top clerics in the conservative Islamic kingdom, which issued a statement urging all other Muslim states to join the coalition.

Jubeir said the anti-terrorism group would not only include a military, security and intelligence track, but an ideological one as well. Whether more statements by the Wahhabi clergy denouncing militancy will allay Western criticism, though, is doubtful.

Western media often overstate the degree to which Wahhabi teachings resemble the far more extreme positions of Islamic State, and fail to note the war of words and accusations of apostasy between Saudi clergy and jihadist preachers.

But Saudi officials in turn rarely acknowledge the links between militant thought and their own faith's propagation of intolerance towards others.

Modern jihadist groups follow an extreme interpretation of Islam's Salafi branch, of which Wahhabism was the original strain, and whose clerics regard Shi'ism as heresy, laud the concept of jihad, urge hatred of infidels and back harsh penalties for religious offences.

One driving force of support for Islamic State has been a rise in sectarian anger, much of it driven by the proxy wars emerging from a political struggle between Sunni Saudi Arabia and Shi'ite Iran.

In that context, the absence from Riyadh's coalition of Iran and its allies Iraq and Syria seemed to suggest that it may hope eventually to use its Muslim coalition against terrorism as a Sunni bloc that could isolate Tehran's Arab Shi'ite proxies.

Riyadh describes the Lebanese militia Hezbollah and Iraq's Hashd al-Shaabi Shi'ite militias, which have been accused of killing Sunni civilians but are all enemies of Islamic State on the battlefield, as terrorist groups.

"Actually, I think this is partly about Shi'ite terrorism, because nobody is putting any effort into fighting that," said Mustafa Alani, a security expert with close ties to Saudi Arabia's Interior Ministry.

Whether such a goal would be shared by most of Riyadh's new partners in its much vaunted coalition, a group that includes countries which have amicable ties with Iran, appears unlikely.