Muslim leaders and UN Secretary General Ban Ki-moon called at the start of an Islamic summit on Thursday for Israel to halt attacks on Palestinian civilians and for an end to 'Islamophobia' by the West.

But new tensions between Chad and Sudan cast a shadow over the start of the 57-nation Organisation of the Islamic Conference meeting amid new efforts by the UN chief and the Senegalese hopes to bring the bitter rivals together.

The UN Secretary General Ban renewed his condemnation of Israel's attacks on Palestinian civilians in his speech to the 11th OIC summit.

"Israel's disproportionate and excessive use of force has killed and injured many civilians, including children. I condemn these actions and call on Israel to cease such attacks," Ban told an audience that included Palestinian president Mahmud Abbas.

"At the same time, I also condemn the rocket attacks directed against Israel and call for the immediate cessation of such acts. They serve no purpose, endanger Israeli civilians and bring misery to the Palestinian people," he added.

There has been a sharp escalation in violence since the end of February in which more than 130 Palestinians were killed, including dozens of militants, and five Israelis, including four soldiers.

President Abdoulaye Wade of Senegal, head of the OCI for the next year, said he would make efforts to end the Middle East conflict his number one priority.

Wade also urged a ceasefire but called on Israel to end "all of its illegal activities in the occupied territories ... the blind repression inflicted on the Palestinian people."

Many of the leaders at the summit had other conflicts in their territory or nearby to worry about.

Afghanistan President Hamid Karzai was preoccupied with a car bomb in Kabul that killed six people. Iran's President Mahmoud Ahmadinejad was also a key figure at the summit as he confronts tensions with the United States over its nuclear programme.

"We are called upon to summon our potentials to deal with overdue and chronic issues that continue to plague our lives," OIC Secretary General Ekmeleddin Ihsanoglu told the summit, citing conflicts involving members Iraq, Lebanon, Somalia, Comoros and Afghanistan.

Highlighting the troubles that have beset its members, Chad accused rebels backed by neighbouring Sudan of crossing the border to launch an offensive as Chadian President Idriss Deby Itno attended the Dakar meeting.

The rebels denied they had launched any offensive however and Sudan described the allegations as "complete nonsense".

On the eve of the summit, Wade had sought to bring together Deby and Sudan's President Omar al-Beshir for talks on ending bitter rivalry between the two.

But Beshir failed to turn up at the meeting, which also included the UN chief. The Senegalese leader said Beshir blamed "a headache" for his absence.

A meeting between Deby and Beshir started on Thursday amid were widespread doubts that any progress would be made. Chad and Sudan have made five previous accords but at times come close to war in the past five years.

The diplomatic tensions diverted attention from the OIC leadership's efforts to reform the body with a new charter and its campaign against 'Islamophobia' - attacks and threats against Muslims and what it considers insults against the Islamic faith in the West.

The OIC wants western nations to clamp down harder on what it considers anti-Islamic gestures such as the publication of cartoons lampooning the Prophet Mohammed in Denmark and the looming release of an anti-Islamic film by far-right Dutch MP Geert Wilders.

"Freedom of speech should reach the point of attacking or showing disrespect for others point of views," said Saudi Arabia's Foreign Minister Prince Saud al-Faisal in one of many speech which condemned "defamation" of Islam.

The UN chief joined the leaders in expressing disquiet.

"Millions of Muslims around the world want this summit to assure them that we are defending the collective interest against the defamation of the Prophet Mohammed and Muslims in general," said Arab League secretary general Amr Moussa.