President Barack Obama Monday ruled that a regional grouping of Gulf Arab states should be allowed to buy certain US defense articles, deepening ties with a grouping wary of Iran's regional influence.

Obama determined that US restrictions on selling material for ballistic missile defense, maritime security and counter-terrorism operations should be lifted, opening the way to purchases by the six-nation Gulf Cooperation Council (GCC).

The initiative was announced by US Defense Secretary Chuck Hagel earlier this month in the region and Obama's determination is required before military sales can take place under US law.

"I hereby find that the furnishing of defense articles and defense services to the Gulf Cooperation Council will strengthen the security of the United States and promote world peace," Obama said in a memorandum to Secretary of State John Kerry.

The move came amid increasing concerns among America's Gulf allies about the perceived threat from Iran, and was seen in some circles as an attempt by Washington to assure Gulf states that it has not taken its eye of Tehran's regional ambitions despite trying to conclude a nuclear deal with the Islamic Republic.

"Today's action will allow the GCC to pursue the defense articles and services necessary to further regional defense cooperation," said Bernadette Meehan, a National Security Council spokeswoman.

"The designation reflects our strong commitment to the GCC and our desire to work with our Gulf partners to promote long-term regional security and stability."

During his trip to Bahrain, Hagel announced that Washington planned to keep 35,000 troops and an array of military and maritime resources in the region.

Senior officials said his intention was to send a message of solidarity to Gulf allies while also conveying a warning to adversaries "that any sort of mythology of American retreat is just wrong-headed."

US Gulf allies are concerned about the interim nuclear deal with Iran reached in November, the US failure to intervene in Syria over chemical weapons attacks and the US pullback from Afghanistan.

The Pentagon has for years tried to encourage closer security cooperation among the Gulf states, especially on missile defense.

The GCC includes Saudi Arabia, the United Arab Emirates, Qatar, Kuwait, Oman and Bahrain.

Regional states have previously been able to buy US arms and equipment individually, but Monday's determination opens the way to the GCC's first such purchases as a group.