Rebecca Rebarich, Pentagon spokeswoman, expressed that the payment was "the first contribution" in a burden-sharing partnership between the both countries to support regional security.

Saudi Arabia paid Washington a sum of US$500 million last month to cover part of the cost of United States troops stationed in the kingdom as bilateral talks over defense expenses continue, a Pentagon spokeswoman Commander Rebecca Rebarich told Middle East Eye Friday.

The official said that the payment was "the first contribution" in a burden-sharing partnership between both countries to support regional security.

"In response to elevated threats in the Middle East over the past eight months, the Department of Defense has deployed U.S. military forces to the region to enhance U.S. defenses and augment Saudi air and missile defense of critical military and civilian infrastructure," Rebarich explained.

Last week, U.S. President Donald Trump told Fox News that Saudi Arabia had "already deposited US$1 billion in the bank,"

Yet these payments to "offset" military costs are not new. During the first Gulf War in the 1990s, Saudi Arabia, Kuwait, and other Gulf states paid Washington an estimate of US$36 billion.

The U.S. also charged Saudi Arabia US$331 million for the cost of aerial refueling operations that the U.S. military provided to Saudi warplanes carrying out airstrikes in Yemen. Saudi Arabia is the biggest global buyer of U.S. weapons, with its total military spending far surpassing the amount spent by any other country in the region.

It is not clear how much Saudi Arabia will be expected to pay for the U.S.'s increased presence in the region, as tensions between Washington and Tehran leave the Gulf in a precarious situation.

Bilateral talks to determine that amount are ongoing, Rebarich said, adding that the aim is to formalize a mechanism that will determine the scope of future payments to cover some of the costs of U.S. troop build-up.

Since the assassination of Iran's Major-General Qassem Soleimani by the U.S., tensions in the region have only increased. Following his death, Washington sent another 3,000 soldiers to different locations in the Middle East.