The U.S. is sending more troops, missile systems and warplanes to Saudi Arabia amid concerns about Iranian aggression in the region, President Donald Trump said in a letter sent to Congress this week.

Axar.az reports citing Stripes that the new deployments are intended to guard against “hostile action by Iran and its proxy forces” and will bring the total number of troops in Saudi Arabia to 3,000, Trump said in the letter, sent Tuesday.

The increased U.S. presence in the region seeks to “assure our partners, deter further Iranian provocative behavior, and bolster regional defensive capabilities,” Trump wrote. The troops will remain in Saudi Arabia “as long as their presence is required” to fulfill those missions, he wrote.

Some American forces have already arrived in the country while others will be deployed in the coming weeks, Trump said.