GCC countries began "enhanced security patrols" in the international waters of the Arabian Gulf on Saturday, the US Navy's Fifth Fleet said.
GCC members were "specifically increasing communication and co-ordination with each other in support of regional naval co-operation and maritime security operations in the Arabian Gulf", the fleet, based in Bahrain, said on Sunday.
The US announcement came hours after Saudi Arabia announced an emergency summit of Gulf and Arab leaders scheduled for May 30 to discuss recent attacks on Saudi oil installations and commercial vessels off the coast of the UAE.
The kingdom’s foreign ministry made the announcement on Twitter in the early hours of Sunday.
Also on Sunday, the Saudi Media Ministry said Crown Prince Mohammed bin Salman had discussed regional developments and the need to strengthen security in a call to US Secretary of State Mike Pompeo.
Adel Al Jubeir, the Minister of State for Foreign Affairs, spoke a week after four oil tankers, two of them Saudi, were hit in an act of sabotage off the coast of the UAE, and days after Iran-backed Yemeni rebels claimed a drone attack on a Saudi oil pipeline and two pumping stations.
"The kingdom of Saudi Arabia does not want war in the region and does not strive for that," Mr Al Jubeir said.
"But at the same time, if the other side chooses war the kingdom will fight this with all force and determination, and it will defend itself, its citizens and its interests."
Iran's elite Revolutionary Guard Corps is "highly likely" to have orchestrated the attacks last Sunday on the four tankers off Fujairah, said a Norwegian insurers' report seen by Reuters.
The other two vessels in the attack were registered in the UAE and Norway.
The confidential assessment by the Norwegian Shipowners’ Mutual War Risks Insurance Association concluded that the attack was probably carried out by a surface vessel operating close by that sent underwater drones carrying 30 kilograms to 50kg of high-grade explosives to detonate on impact.
The attacks took place at a time of increased US-Iranian tension after Washington’s decision this month to try to cut Tehran’s oil exports to zero and to increase its military presence in the Gulf in response to what it called a "credible threat" from Iran and its proxies.
The US last week withdrew non-essential staff from its embassy in Baghdad claiming security concerns and the oil firm Exxon Mobil removed its foreign staff from southern Iraq.
The Iraq oil minister said Exxon's action was unacceptable and based on political considerations rather security concerns.
Iran's Foreign Minister dismissed the possibility of war in the region.
"There will be no war because neither do we want a war, nor has anyone the idea or illusion it can confront Iran in the region," Javad Zarif told Iran's Irna state news agency in Beijing.
"The fact is that Trump has officially said and reiterated again that he does not want a war, but people around him are pushing for war on the pretext that they want to make America stronger against Iran."
But Maj Gen Hossein Salami, commander of the Revolutionary Guard, said Tehran would defeat the US in an intelligence war, Iran's Fars news agency reported.
"We are able to defeat the enemy in an intelligence war. Breaking the enemy's will to use power means disarming the enemy," Gen Salami said.
He said an intelligence war included psychological and cyber operations, military moves and public diplomacy, and that despite its "ostentatious appearance", the US was suffering from "osteoporosis".
Egyptian President Abdel Fattah El Sisi held talks on Saturday with Saudi ambassador Osama Al Nugali and voiced his support for Gulf nations amid the regional developments.
Mr El Sisi said Egypt would stand against those looking to create instability.
Sheikh Mohamed bin Zayed, Crown Prince of Abu Dhabi and Deputy Supreme Commander of the Armed Forces, met Mr El Sisi in Cairo last week.
The discussions between Sheikh Mohamed and Mr El Sisi "touched on the latest crisis that Arab countries are experiencing" where they supported efforts to find "political solutions" for them, a presidential statement said.
Bahrain on Saturday warned citizens against travelling to Iran and Iraq and asked those in the countries to leave.
The US embassy in Iraq last week ordered all "non-essential" staff to leave the country immediately.
Meanwhile, Iranian President Hassan Rouhani said on Saturday that Tehran would not be bullied into negotiating, Irna reported.
"The US claim that it is forcing us to the negotiating table is worthless," Mr Rouhani said.
"We are for logic, negotiation and dialogue but we will never surrender to anyone who intends to bully us."
Battered by US sanctions and an ailing economy, Iran's rial has fallen to 148,000 to the American dollar.
That compared with 32,000 in 2015 when international sanctions were lifted following a deal to curb its nuclear programme. Many Iranians have seen their life savings wiped out as a result.
Nationwide, the unemployment rate is 12 per cent. For youth it is even higher, with a quarter of all young people unemployed, Iran's statistic centre says.