KUWAIT, March 25 (Sylvia Westall and Amena Bakr/Reuters) - Warning of enormous dangers, Kuwait urged fellow Arab leaders on Tuesday to resolve disputes complicating crises such as Syria's war and unrest in Egypt, but diplomats said tensions bubbled behind the scenes at an annual heads of state summit.

The gathering of the 22-member Arab League also heard an appeal from the U.N. peace mediator for Syria, Lakhdar Brahimi, for an end to the flow of arms to the combatants in the war, which has killed over 140,000 people and displaced millions.

Brahimi did not identify the suppliers, but Saudi Arabia and Qatar are believed to be the main Arab funders of military assistance to rebels in Syria, while non-Arab Iran is the main regional power backing President Bashar al-Assad.

The whole region is in danger of being dragged into the conflict, Brahimi said, calling for renewed efforts to find a political settlement to the crisis, now in its fourth year.

Kuwait's emir, Sheikh Sabah al-Ahmad al-Sabah, urged Arab states to overcome rifts he said were blocking Arab initiatives. The dangers around us are enormous and we will not move towards joint Arab action without our unity and without casting aside our differences, Sheikh Sabah, the summit host, said.

He named no country. But he was alluding to worsening disputes among Arab states over the political role of Islamists in the region, and over what many Gulf states regard as interference in their affairs by Shi'ite Muslim Iran, locked in a struggle for regional influence with Sunni rival Saudi Arabia.

Participants said there were differences over Qatari support for the outlawed Muslim Brotherhood in Egypt, how to deal with the Syria crisis and how to define terrorism in the region.

Behind closed doors there is tension, but it's all under the table, no confrontation was made (in public), one of the diplomats said. There are clear divisions over what Saudis and the Qataris think.

CONSENSUS ELUSIVE?

In another sign of brewing discord, some delegates said it was possible the summit would take the rare step of not issuing a final communique, suggesting consensus was proving elusive.

The summit followed an unusual dispute within the Gulf Cooperation Council alliance of Gulf Arab states over Qatari support for Egypt's Muslim Brotherhood, and a spat between Iraq and Saudi Arabia over violence in Iraq's Anbar province.

Another diplomat said: There were heated remarks about Egypt behind closed doors. Qatar has made comments about how things should happen in Egypt and Egypt says it is for them to decide.

The Gulf states' hereditary ruling families tend to keep their disputes private, meaning that a move by Saudi Arabia, the United Arab Emirates and Bahrain this month to recall their ambassadors from Qatar was highly sensitive.

The three accuse Doha of interfering in their internal affairs and giving support to Islamist groups whose republican, revolutionary views they see as a political menace. Qatar denies it interferes anywhere but vows no change in its foreign policy.

Kuwait has offered to mediate: At the summit opening, Sheikh Sabah, smiling broadly, stood between Saudi Crown Prince Salman and Qatar's emir, Sheikh Tamim bin Hamad al-Thani, holding hands with them in an attempt to convey a mood of reconciliation.

But government officials said Kuwait's emir did not carry out any mediation attempts on the sidelines of the main meeting.

Tamim seemed to signal his views were not likely to change.

In his speech, Tamim said that while he respected what he called the Egyptian people's choice, he was calling for comprehensive political and social dialogue - remarks that will be seen as a recommendation that the military-backed Egyptian government reverse its ban on the Brotherood.

Qatari-Egyptian ties have soured since the Egyptian army ousted Islamist President Mohamed Mursi, who had been supported by Doha, in July after mass protests against his one-year rule.

STRAINED RELATIONS

Arab summits are often dominated by the Israeli-Palestinian conflict, a unifying topic for Arabs. The Arab Spring uprisings that began in 2011 have polarized the region, however.

Syria's war has strained ties between Sunni Muslims, notably in the Gulf, and Shi'ite Muslims in Iraq, Lebanon and Iran, whose faith is related to that of Assad's Alawite minority.

Reiterating that he saw no military solution to the war, Brahimi said Lebanon was in particular danger of being sucked into the increasingly sectarian conflict.

Saudi Crown Prince Salman called for changing the balance of forces on the ground in Syria, adding that the crisis in Syria had reached catastrophic proportions. Salman later left Kuwait, soon after he delivered his speech. Veteran Foreign Minister Prince Saud al-Faisal remained in Kuwait, an aide said.

The meeting was expected also to address other challenges such as Iran, whose long frosty relations with the West have thawed since the election of moderate President Hassan Rouhani.

Syrian opposition leaders have been lobbying the Arab League to give them Syria's seat on the pan-Arab body, and to push Arab states to approve the delivery of military hardware to them.

Syria's seat remained vacant during the summit session on Tuesday, something Ahmed al-Jarba, head of the opposition Syrian National Coalition, said would benefit, not punish, Assad contrary to what the League intended in suspending Damascus.

Leaving Syria's seat empty sends a message to al-Assad...'kill, kill, (and) the seat is waiting for you once the battle is settled', Jarba told the summit.

Syria's Arab allies, including Iraq, Algeria and Lebanon, oppose support for the rebels. They point out that Islamists, including groups linked to al Qaeda, constitute the strongest force in the armed opposition. (Additional reporting by Sami Aboudi and Rania El Gamal in Dubai, Samia Nakhoul and Dominic Evans in Beirut, Editing by William Maclean/Mark Heinrich)