Attacks against targets in Saudi Arabia by the Yemeni rebel group, Houthis, have doubled in the first nine months of 2021 compared to the same period in 2020, according to a report released Tuesday.

The Houthis are "orchestrating an increasingly intense irregular warfare campaign against Saudi Arabia and other countries in the Gulf," said the report by the US-based, The Center for Strategic and International Studies (CSIS) think tank.

It said Iran’s Islamic Revolutionary Guard Corps-Quds Force and Lebanese Hezbollah have played a critical role in providing weapons, technology, training, and other assistance to the group.

The CSIS said it analyzed 4,103 Houthi attacks against Saudi Arabia, within Yemen, and against other targets in the Gulf between Jan. 1, 2016, and Oct. 20, 2021.

According to the research, during the first nine months of 2020, Houthi forces executed a monthly average of 38 attacks but during the same period in 2021. That number rose to an average of 78 attacks, for a total of 702 attacks across the nine-month period.

"This increase was largely driven by the Houthi offensive in Marib, where 199 attacks took place during the first nine months of 2021," it said.

"Houthi forces also carried out 133 total attacks in August 2021 alone—the highest single-month tally since at least January 2016. These attacks, however, were not equally distributed across geographic areas," it added.

Yemen has been engulfed by violence and instability since 2014, when Iran-aligned Houthi rebels captured much of the country, including Sana’a.

A Saudi-led coalition aimed at reinstating the Yemeni government has worsened the situation, causing one of the world’s worst man-made humanitarian crises, with nearly 80%, or about 30 million people, needing humanitarian assistance and protection and more than 13 million in danger of starvation, according to UN estimates.

A recent UN report projected that by the year’s end, the death toll from the seven-year conflict will reach 377,000./agencies