The US has ruled out a military pact with the Arab Gulf states citing the complexities of forming a treaty in the Middle East.

Ben Rhodes, the US deputy national security adviser for strategic communication, told Al Jazeera's Patty Culhane on Wednesday the US was committed to the defence of Gulf Cooperation Council (GCC) countries but a formal treaty would not happen in the near future.

"A treaty is not what we're looking for. It took decades to build NATO and the Asian allies but we can provide clear assurances that we will come to their defence," Rhodes said, alluding to a prospective alliance with the Gulf countries.

President Obama spoke by phone today with King Salman of Saudi Arabia to discuss upcoming GCC Summit. Readout to come — Ben Rhodes (@rhodes44) May 11, 2015

The comments came a day before US President Barack Obama meets leaders of the GCC at a summit at Camp David in Maryland.

Gulf and US leaders are expected to address the former's security concerns, with tensions heightened between the regional powers because of Iran's support for Houthi fighters in Yemen and the Assad government in Syria.

An Arab military coalition has launched air strikes in Yemen to halt a Houthi offensive and restore the government of exiled President Abd-Rabbu Mansour Hadi.

Both Saudi Arabia and Qatar also back Syrian fighters battling to overthrow the Iranian-backed Syrian government.

The countries are expected to press the US for a written commitment to defend them in case of an Iranian attack.

In a related development, Iran has announced it is sending an aid ship to Yemen, prompting a fresh war of words with the US.

Iranian Brigadier-General Masoud Jazayeri warned the US against stopping the ship, after the US said it was tracking its movements.

Jazayeri said that if Saudi Arabia or the US "continue to create obstacles on Iran's aid delivery, a fire might start that would definitely be out of their control".