Forces from 20 countries arrived in Saudi Arabia to participate in a major military drill in the Gulf powerhouse.The exercise, dubbed "Northern Thunder", will be held in northern Saudi Arabia and will see the participation of forces from Arab and Islamic countries, the official Saudi Press Agency said on Sunday. SPA described the military drill as "the most important and the biggest in the history of the region."Forces from Saudi Arabia, the United Arab Emirates, Jordan, Bahrain, Senegal, Sudan, Kuwait, the Maldives, Morocco, Pakistan, Chad, Tunisia, Comoros Islands, Djibouti, Oman, Qatar, Malaysia, Egypt, Mauritania and Mauritius will participate in the event. SPA said the drill "represents a clear message that Saudi Arabia and its brothers and friends of the participating countries stand united to confront all challenges and maintain peace and stability in the region." Saudi Arabia is leading a military campaign against the Iran-backed Shia Houthi group, which seized control of Yemeni capital Sanaa in late 2014. Last December, it also formed a new 35-member coalition to fight 'terrorism'. SPA said that the exercises in the country's north will include air, sea and land forces. They are expected to last 18 days, with participating forces arriving in "the next few hours." Most of the participants are Arab and African countries, and do not include the United States and other Western powers.