DAKAR, Senegal - Senegal's president, the new chairman of the world's largest Muslim group, said Thursday he would make solving the long-standing Israeli-Palestinian crisis a priority for the organization. A separate attempt to broker peace between two feuding African neighbors gained fresh urgency as Chad accused Sudan of aiding a new rebel advance.

"The just and legitimate cause of Palestine remains at the heart of our concerns," Abdoulaye Wade told the leaders of dozens of Islamic nations in Senegal's seaside capital as a two-day Organization of the Islamic Conference summit began.

Wade called Israel "an occupying power" and urged its government to "immediately stop its disproportionate use of force."

He added: "I should like to tell our brothers and sisters of Palestine that your unity is the first priority of success .... Please unite."

The Middle East has long been a core issue for the 57-member OIC, which was founded in 1969 in response to an arson attack on the al-Aqsa mosque in Jerusalem. The group aims to promote Islamic unity and serve as a voice for the Muslim world.

Wade has tried to cast himself as a continental peacemaker and had hoped to bring the president's of Chad and Sudan together to sign a peace deal on the eve of the summit. But Wednesday's talks were canceled after Sudanese leader Omar al-Bashir, who was in Dakar, failed to show. Al-Bashir said he had a headache and was too tired after a long journey.

According to a Chad government statement Thursday, Sudan launched "several heavily armed columns" against Chad on Wednesday. The Chadian government called the fighters "mercenaries," its term for Chadian rebels it accuses Sudan of backing, and said they had crossed from Sudan and reached a border town, Moudeina.

The leaders of Chad and Sudan have long traded acrimonious accusations of supporting each other's rebel groups.

Chad President Idriss Deby has accused Sudanese authorities of arming rebels who launched a failed assault last month on the Chadian capital, N'Djamena. The rebels reached the gate of the presidential palace, but fled toward Sudan after Chad's army repelled them in fighting that left hundreds dead. Sudan, meanwhile, has repeatedly accused Chad of supporting Darfur rebels.

The deal proposed by Senegal would have aimed to commit them to implementing earlier, faltered, accords in a step toward calming Darfur and other areas on their shared border. Talks were expected to go forward Thursday on the sidelines of the summit.

The Palestinian delegation declared the summit a success even before it began, saying earlier Thursday it had garnered key support from fellow Muslims.

A declaration drafted by foreign ministers to be adopted by the summit "reinforces support and backs Palestine, and condemns Israel for what it is doing in Gaza," Palestinian Foreign Minister Riad Malki said as leaders of dozens of Islamic nations gathered in Senegal's capital for the opening of a two-day Organization of the Islamic Conference summit.

Malki called the summit "an exercise in solidarity and in showing political support for countries like Palestine."

The Middle East long has been a core issue for the 57-member OIC, the world's largest Muslim grouping. It was founded in 1969 in response to an arson attack on the al-Aqsa mosque in Jerusalem. The group aims to promote Islamic unity and serve as a voice for the Muslim world.

Summits are traditionally held every three years, and the agenda this year included studying ways to improve Islam's image in the West and spurring economic development in some of the world's poorest countries - the summit brings together Arab countries that set the price of oil with small African nations who struggle to provide their citizens with paved roads.

The crises likely to be addressed on the sidelines of the summit are some of the world's most intractable.

The protracted war in Iraq continues to dominate international headlines, and organizers say it will be on the agenda along with the conflict between the Palestinians and Israel. This week, delicate attempts by Egypt to negotiate peace there were threatened by a rocket attack by a Palestinian militant group near the Israeli city of Ashkelon. The West Bank-based Palestinian government has accused Israel of endangering the peace process with new plans for settlement expansion.

The OIC summit was returning to Africa for the first time in 14 years. Some 40-odd heads of state are attending, including Iranian President Mahmoud Ahmadinejad and Algerian President Abdelaziz Bouteflika. The Palestinian delegation was led by President Mahmoud Abbas, and Iraq's by Prime Minister Nouri Maliki. U.N. Secretary-General Ban Ki-moon also was attending.

For the first time, the U.S. sent a representative. The U.S. government has said it appointed Texas entrepreneur Sada Cumber to the Islamic group "to promote mutual understanding and dialogue between the United States and Muslim communities."

Arguments over the way Islam is portrayed in the West continue to cause anger within the Muslim world. In recent weeks, the republication of political cartoons depicting Prophet Muhammad by Danish newspapers sparked protests in Pakistan, Afghanistan, Jordan, Thailand, Iran and Sudan.

OIC delegations will consider a report compiled for the summit that is an attempt to comprehensively record anti-Islamic speech and action around the world. The report calls for Muslim nations to take legal action against such acts.

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Associated Press Writer Rukmini Callimachi contributed to this report.