RIYADH: Warplanes roared overhead, tanks rumbled across the desert and smoke filled the sky Thursday for the final day of what Saudi Arabia billed as the region's biggest-ever military exercises.

The 12-day “Northern Thunder” manoeuvres in the kingdom's northeast included 20 nations from the Middle East, Africa and Asia, Saudi officials said.

Saudi Arabia's King Salman was joined by several foreign leaders for the final day of the exercise, which came as Riyadh vies to assert its leadership in the region.

Among them were Egypt's President Abdel Fattah al-Sisi, Sudan's Omar al-Bashir, Yemen's Abedrabbo Mansour Hadi and Pakistani Prime Minister Nawaz Sharif.

As the dignitaries watched from a pavilion, Apache gunships fired rockets with a bone-shaking blast. Smoke rose from targets on the ground and commandos rappelled from helicopters.

Fighter jets streaked through the sky releasing orange flares, artillery shells whistled through the air and heavy machinegun fire boomed from across the drill site, which stretched for dozens of kilometres (miles). The exercises took place near Hafr al-Batin city, close to the Kuwaiti and Iraq borders.

Saudi Arabia's chief of staff, General Abdulrahman al-Bunyan, commanded the exercise and called it “the largest Arab and Islamic military gathering” in the region.

An AFP reporter saw Pakistani, Egyptian, Kuwaiti and Sudanese troops alongside Saudis.

A foreign military source told AFP he did not think Northern Thunder was directed at Syria "or anything else" but was a chance to practise working together.

The source said Saudi troops were "honing their skills and their operability with other nations."

Northern Thunder's official Twitter account said the exercises aimed to "confront all the threat scenarios in the region".