Arab and Muslim leaders began gathering in the holy city of Mecca on Thursday for three summits, as host Saudi Arabia seeks to rally support against Iran after a series of attacks that have sparked fears of a regional conflagration.

That call came just hours after hawkish US National Security Advisor John Bolton said Iran was almost certainly behind the sabotage of four ships, including two Saudi oil tankers, off the UAE coast.

Iran-aligned Yemeni rebels meanwhile have stepped up drone attacks on the kingdom -- one of which resulted in the temporary shutdown of a major oil pipeline.

Saudi Arabia, a staunch US ally, geared up to host leaders from across the Arab and Muslim world for emergency Gulf and Arab summits and a meeting of heads of state from Islamic nations.

Egypt's President Abdel Fattah al-Sisi, Kuwait's emir, Sheikh Sabah Al-Ahmed Al-Sabah, and Sudan's new military council chief General Abdel Fattah al-Burhan were among the leaders arriving in the kingdom Thursday, Saudi state media reported.

Riyadh called the talks to discuss the standoff with Iran and ways of isolating Tehran amid fears of a military confrontation.

"Tehran's support for Huthi rebels in Yemen is proof of Iranian interference in other nations' affairs and this is something that... Islamic countries should reject," Saudi Foreign Minister Ibrahim al-Assaf told foreign ministers from the 57-member Organisation of Islamic Cooperation in Jeddah overnight.

Assaf said attacks on oil installations must be addressed with "firmness and determination".

Contrary to expectations, Iran was represented at the meeting, with a delegation headed by Reza Najafi, director general for international peace and security affairs at the Islamic republic's foreign ministry.

Tensions in the region spiked after the four ships were damaged in a mysterious sabotage attack off the coast of the emirate of Fujairah on May 12.

The vessels were attacked using "naval mines almost certainly from Iran", Bolton told a news conference in Abu Dhabi on Wednesday.

"There's no doubt in anybody's mind in Washington who's responsible for this," he said in a clear reference to Iran.

Iran rejected the accusation.

"Making such laughable claims... is not strange" coming from the US, foreign ministry spokesman Abbas Mousavi said.

US experts are part of a five-nation team investigating the ship attacks. The new war of words between Tehran and Washington follows a US military buildup that includes the deployment of an aircraft carrier, B-52 bombers and 1,500 more troops to the region.

Bolton however said the additional US forces were sent to the Middle East as a "deterrent" and that Washington's response would be prudent.

"We definitely desire a change in the (Iranian) regime's behaviour," Brian Hook, US Special Representative for Iran, said Thursday.

Regional tensions have grown since US President Donald Trump's administration reimposed sanctions against Iran after Washington unilaterally pulled out of a multilateral 2015 nuclear accord signed with the Islamic republic.

But Trump appeared to soften his hawkish tone towards Tehran, saying during a visit to Japan on Monday that his government does not seek "regime change".

Saudi Arabia is hosting the three summits in an apparent bid to present a unified front against Tehran.

Qatar's state media reported that its Prime Minister Sheikh Abdullah bin Nasser al-Thani also arrived in Jeddah on Thursday, Doha's highest-ranking official to visit the kingdom since the start of a two-year-old Saudi-led boycott.

Saudi Arabia, the UAE, Bahrain and Egypt have enforced the economic and diplomatic boycott of Qatar since June 2017, including bans on shipping, trade, direct flights, overflight and land crossings.

The alliance accuses Doha of supporting Islamist movements and backing Iran -- claims Qatar rejects.

Large banners and flags decorated the streets of Mecca, Islam's holiest city, to welcome the leaders.

The summits coincide with the last few days of the Muslim fasting month of Ramadan, when Mecca throngs with hundreds of thousands of pilgrims.

The summits will take place at night, as Muslims break their day-long fasting at sunset and then go into several hours of special prayers known as Taraweeh.

Drapped in seamless all-white uniforms, worshippers walked under lampposts decorated with flags of participating nations, while heading to the Grand Mosque to perform umrah, the minor Islamic pilgrimage.

The large crowds pose a logistical headache for organisers, who have sealed off six major roads for the leaders and advised pilgrims to use alternative streets.

(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)