U.S. Defense Secretary Mark Esper arrived in Saudi Arabia on Monday, with tensions simmering between Washington and Tehran, and Russia seeking to boost its influence in the Middle East.

Axar.az reports citing Reuters.

Esper is likely to meet King Salman and Crown Prince Mohammed bin Salman on his first trip to the key regional ally since taking office this summer, a visit intended partly to reassure Riyadh over bilateral ties.

Upon landing in Riyadh, he met the head of U.S. Central Command, which is responsible for military operations in the Middle East and Afghanistan.

U.S.-Iran tensions have risen to new highs since May 2018, when the Trump administration withdrew from an international accord that put limits on Tehran’s nuclear program in exchange for easing sanctions.

As reinstated sanctions put pressure on Iran’s economy, there have been a series of attacks which Washington and close allies blame on Tehran. Iran denies responsibility.

The United States has deployed about 3,000 additional military forces since May to bolster Saudi defenses, including an air expeditionary wing and air defense personnel.

Despite the additional troops, President Donald Trump’s sudden withdrawal of forces from northeastern Syria has raised questions about Washington’s commitment to allies and opened the door for Russia to increase its regional influence.

The move was criticized as a betrayal of Kurdish allies who fought for years alongside U.S. troops against Islamic State. Esper said on Monday that at least some troops might stay to deny Islamic State and others access to oil fields.