DOHA, Qatar — A Syrian opposition leader, taking Syria's seat at an Arab summit for the first time on Tuesday, said the United States should use Patriot missiles to protect rebel-held areas from President Bashar al-Assad's air power.

Moaz Alkhatib said he had asked Secretary of State John Kerry for U.S. forces to help defend rebel-controlled northern parts of Syria with Patriot surface-to-air missiles.

The insurgents have few weapons to counter Assad's helicopter gunships and warplanes.

Alkhatib said the United States should play a bigger role in helping end the two-year-old conflict in Syria, blaming Assad's government for what he called its refusal to solve the crisis.

"I have asked Mr Kerry to extend the umbrella of the Patriot missiles to cover the Syrian north and he promised to study the subject," Alkhatib said, referring to NATO Patriot missile batteries sent to Turkey last year to protect Turkish airspace.

"We are still waiting for a decision from NATO to protect people's lives, not to fight but to protect lives," he said.

The Sunni Muslim cleric took over Syria's vacant chair at the Arab League summit in Doha despite announcing on Sunday that he would step down as leader of the Syrian National Coalition.

The emir of Qatar, a strong supporter of the struggle to topple Assad, asked his fellow-Arab leaders to invite the coalition delegation to represent Syria formally at the summit, despite the internal divisions plaguing the opposition.

The Arab League suspended Syria in November 2011 in protest at its use of violence against civilians to quell dissent.

In his opening speech, Qatar's Sheik Hamad bin Khalifa al-Thani urged the U.N. Security Council to stop the "oppression and repression of the people" in Syria, halt the bloodshed and "present those responsible for these crimes against their people to international justice."

The United Nations says about 70,000 people have been killed in a conflict that began with peaceful anti-Assad protests and turned into an increasingly sectarian armed insurrection.

The war in Syria has divided world powers, paralyzing action at the Security Council. The Arab world is also split, with Saudi Arabia and Qatar the most fervent foes of Assad, and Iraq, Algeria, and Lebanon the most resistant to calls for his removal.

INTERNAL DISARRAY

Alkhatib's decision to quit, which he blamed on the world's failure to back the armed revolt against Assad also appeared to be motivated by internal disputes in the alliance. It undermined the alliance's claim to provide a coherent alternative to Assad.

Liberals interpreted it as a protest against what they see as the increasing influence of hardline Islamists in the Qatari-backed umbrella group set up in Doha in November to replace the ineffectual Syrian National Council.

Syria's Muslim Brotherhood, criticized for its grip on the Syrian National Council, appears to be wield as much sway on its successor coalition, which has won wide international backing, but has failed to shake an image as consisting mostly of foreign-backed exiles immersed in political infighting.

Alkhatib, a former imam at the Umayyad Mosque in Damascus, had told Al Jazeera television before the summit that his main reason for quitting was frustration with world inaction.

He criticized "states which are only trying to push through their wishes, aspirations or ways to solve the [Syrian] crisis without feeling the pain that people suffer every day."

Moderate civilian and military factions in his hometown of Damascus on Monday urged him to reconsider his decision to quit.

On Al-Jazeera, Alkhatib acknowledged the coalition had been divided over whether to set up an interim government, referring to last week's decision in Istanbul to appoint Islamist-leaning technocrat Ghassan Hitto as provisional prime minister.

Apart from Syria, the Arab summit will also discuss stalled Israeli-Palestinian peace efforts and long-standing plans to restructure the Arab League.