GAZA, Jan 30 (Reuters) - The leader of Hamas in the Gaza Strip, Ismail Haniyeh, left on Monday for a tour of Iran and Gulf states, continuing a diplomatic drive to realign the Palestinian Islamist movement after a year of political change in the Arab world.

Non-Arab Iran, along with its Arab ally Syria, have been principal backers of Hamas. Iran has supplied funds and - according to Israel - weapons to use against the Jewish state.

Hamas spokesman Taher al-Nono said Haniyeh, who travels via Egypt since Israel bars other exits from Gaza, was going to Tehran at the invitation of President Mahmoud Ahmadinejad. But he gave no details of the agenda for talks in Tehran.

The upheavals across the Middle East are obliging the Palestinians and their rival political movements, Hamas and Fatah, to review alliances - though how Hamas may adjust its strategies, or its stance towards Israel, is far from clear.

Among Hamas's challenges is financing. A diplomatic source told Reuters that Iran had funded Hamas in the past with up to $300 million per year, but the flow of money had not been regular in 2011. "Payment has been in suspension since August," said the source, who spoke on condition of anonymity.

Iran is under tough international economic sanctions over suspicions, which it denies, that it is secretly developing nuclear weapons in violation of international agreements.

Analysts and diplomatic sources say Iran is unhappy with Hamas for its refusal to offer public support to its ally, Syrian President Bashar al-Assad, who has hosted the Hamas leadership in exile in his capital Damascus for the past decade.

Diplomatic and intelligence sources say Hamas leader Khaled Meshaal no longer spends much time in Syria, where over 5,000 people have been killed in 10 months of conflict.

In a Middle East increasingly divided on sectarian lines between Sunni and Shi'ite Muslim powers, Meshaal appears politically embarrassed by finding his group, which like most Palestinians is Sunni, hosted by a Syrian government dominated by Assad and his Alawite minority, whose sect has its roots in the Shi'ite Islam practised in non-Arab Iran.

Tehran's other Arab allies include Lebanon's Shi'ite Hezbollah movement and Iraq's Shi'ite-led government.

MUSLIM BROTHERHOOD

As the Palestinian offshoot of the Muslim Brotherhood, the Sunni Islamist movement founded in Egypt in the 1920s, Hamas has found itself allied to the very forces - Assad and his Iranian backers - which are cracking down on the Brotherhood in Syria.

However, Hamas said in a statement in recent days that Meshaal's absence from Damascus was due only to concerns about security in that country at the moment and denied that it had moved its leadership or headquarters out of Syria for good.

Arab League states, joining calls from Western powers, have now urged Assad to step aside, deepening Syria's isolation from the rest of the Arab world, where Sunni rulers like those of wealthy Saudi Arabia and populous Egypt are dominant.

Analysts suggest these developments have persuaded Meshaal that Hamas needs to reassess its alliances, and adopt a more conciliatory stance towards the West, which like Israel labels his movement a terrorist group and refuses to negotiate with it.

Meshaal on Sunday visited Western-backed King Abdullah of Jordan, ending a decade-long rift after the monarchy expelled Hamas. Jordan, which has a peace treaty with Israel, was among the first Arab states to call on Assad to step down.

Hamas denies any internal dissent over the movement's future course in light of the changes brought about by the Arab Spring uprisings against entrenched rulers. But analysts say divergences in its collective leadership are clear to see.

London-based Palestinian commentator Ibrahim Hamamy wrote of Haniyeh: "I urge you to reconsider your decision and your program to visit Iran, which took a clearly hostile position against the aspirations of the courageous Syrian people."

Haniyeh was also due to visit the Gulf emirate of Qatar, one of Assad's most vocal opponents in the Arab world.

He earlier visited Egypt and Tunisia to meet fellow Islamist leaders brought to power by last year's uprisings. He also visited Turkey which, unlike its fellow NATO members, recognises Hamas as a legal political party.

Some diplomatic sources have said that Turkey promised to provide Haniyeh's Gaza Strip administration with $300 million to support its annual budget.