Iranian President Mahmoud Ahmadinejad is to attend an extraordinary summit of Muslim leaders in the holy city of Mecca next week at the invitation of the Saudi king, an aide said on Monday.

Ahmadinejad will attend the summit "to discuss the development in Muslim countries," Mohammad Reza Forqani, head of international affairs in the president's office, told the official IRNA news agency.

Forqani said the two-day summit will start on 14 August.

Saudi Arabia last month called for the summit with the aim of "unifying the ranks" of Muslims. It hosts the headquarters of the 57-member pan-Muslim body, the Organisation of Islamic Cooperation, in the Red Sea city of Jeddah.

King Abdullah invited Ahmadinejad, the official Saudi Press Agency reported on Sunday, despite heightened tensions between the Sunni-dominated kingdom and the predominantly Shiite Islamic republic.

In late 2011, US accusations of an Iranian plot to assassinate the Saudi ambassador to Washington angered Riyadh, despite denials from Tehran that it had any involvement.

The two regional powerhouses have also failed to find common ground over uprisings in Bahrain and Syria, respectively Saudi and Iranian allies.

In Bahrain, Iran says it morally supports a Shiite-led protest movement which Saudi Arabia sent troops to crush last year.

In Syria, the kingdom has called for arming rebels against the regime of President Bashar Al-Assad, Iran's staunchest ally in the region.

A big increase in Saudi oil in the market at a time when Western sanctions are hampering Iran's crude exports has also angered Tehran.