US President Barack Obama is sending a foreign policy aide to key Gulf allies Saudi Arabia and the United Arab Emirates this week amid concern over the turmoil sweeping the Middle East.

National Security Advisor Tom Donilon will leave on Monday on a three-day trip during which he will meet Saudi King Abdullah in Riyadh and Crown Prince Sheikh Mohammed bin Zayed al-Nahayan in Abu Dhabi, the White House said.

“The National Security Advisor’s visit underscores the importance of our relationship with these two key partners,” a written statement said.

Saudi Arabia’s intervention last month in Bahrain amid Shiite-led opposition violence has exposed festering political differences between Riyadh and the United States over the revolts rocking the Arab world.

US Secretary of Defense Robert Gates held talks in Riyadh on Wednesday with King Abdullah, with both sides concerned as well by Iranian intentions in the region and spiraling unrest in Yemen.

Boosted by the arrival of a Saudi-led Gulf forces contingent, Bahraini security forces smashed a month-old protest mid-March in central Manama by Shiites, leaving three protesters and two police dead.

The surprise Saudi decision to lead a regional mission into the strife-torn and strategic kingdom ruled by a Sunni minority also reflected the deep shadow cast by Iran in the instability testing US-allied leaders across the Gulf.

Washington appeared to have had little if any advance notice of what was a potentially embarrassing move for the United States, which has led a prolonged effort to prod Bahrain towards political reforms.

Saudi Arabia and other Gulf Arab states have traded accusations with Iran of meddling and interference, especially over Bahrain, which lies off the eastern Saudi coast and is home to the US Fifth Fleet.

“We already have evidence that the Iranians are trying to exploit the situation in Bahrain and we also have evidence that they’re talking about what they can do to create problems elsewhere,” Gates said after Wednesday’s meeting in Riyadh.

King Abdullah’s return home in February after months of treatment abroad for a back ailment came amid mounting international anger over bloodshed in the kingdom’s southern neighbor Yemen.

Yemeni President Ali Abdullah Saleh, a close US and Saudi ally, has faced months of protests calling for his departure, in which around 125 people have been killed.

Dozens of anti-regime demonstrators were shot Sunday in the latest clashes with security forces, sparking charges of “massacre,” as Yemen’s worried Gulf neighbors gathered in Riyadh to work out a transition plan.

The United States announced last year that it plans to offer Saudi Arabia $60 billion worth of hi-tech fighter jets and helicopters, in the largest US arms deal ever.

Violence in Libya and Bahrain has claimed scores of lives and left many more injured as the two Arab countries were united by popular protests that continue to shake the status quo and sound alarm bells across the region and the world.

A week after Egypt’s president, Hosni Mubarak, was forced to stand down, dozens of Libyans were reported killed by Muammar Gaddafi’s security forces. Meanwhile, Bahraini troops shot dead at least one protester and wounded 50 others after mourners buried four people who were killed on Thursday in the worst mass unrest the western-backed Gulf state has ever seen.

“We don’t care if they kill 5,000 of us,” a protester screamed inside Salmaniya hospital, which has become a staging point for Bahrain’s raging youth. “The regime must fall and we will make sure it does.”

Last night footage was posted on YouTube apparently showing Bahraini security forces shooting protesters.

Western nations have been struggling to adjust their policies in response to the security crackdowns in Arab countries.

But Britain announced that it was revoking 44 licences for the export of arms to Bahrain amid concern over the violent suppression of protests in the Gulf state. The Foreign Office also said that eight arms export licences to Libya had been withdrawn, while a review of arms exports to the wider region continues.

Bahrain’s crown prince Sheikh Salman bin Hamad al-Khalifa went on television to promise a national dialogue once calm has returned. But the country’s most senior Shia cleric, Sheikh Issa Qassem, condemned attacks on protesters as a “massacre” and said the government had shut the door to such dialogue.

While the unrest in Bahrain was broadcast instantly around the world, the unprecedented bloodshed in the remote towns of eastern Libya was far harder for global media to cover.

Amid an official news blackout in Libya, there were opposition claims of 60 dead as diplomats reported the use of heavy weapons in Benghazi, the country’s second city, and “a rapidly deteriorating situation” in the latest – and the most repressive – Arab country to be hit by serious unrest.

Libyans said a “massacre” had been perpetrated in Benghazi, al-Bayda and elsewhere in the region. Crowds in the port city of Tobruk were shown destroying a statue of Gaddafi’s Green Book and chanting, “We want the regime to fall,” echoing the slogan of the uprising in Egypt.

Umm Muhammad, a political activist in Benghazi, told the Guardian that 38 people had died in the city. “They [security forces] were using live fire here, not just teargas. This is a bloody massacre – in Benghazi, in al-Bayda, all over Libya. They are releasing prisoners from the jails to attack the demonstrators.” Benghazi’s al-Jala hospital was appealing for emergency blood supplies to help treat the injured.

News and rumours spread rapidly via social media websites including Twitter and Facebook, but information remained fragmentary and difficult to confirm.

In Yemen at least five people were reported killed when security forces and anti-government protesters clashed for a seventh consecutive day in the capital, Sana’a, Aden and other cities, with crowds demanding an end to President Ali Abdullah Saleh’s 32-year rule.

Barack Obama said he was “deeply concerned” about the reports of violence from Bahrain, a close ally and the base of the US fifth fleet, as well as those from Libya and Yemen, and he urged their rulers to show restraint with protesters.

Navi Pillay, the UN high commissioner for human rights, also condemned the killings of protesters in Algeria, Bahrain, Iran, Iraq, Libya and Yemen. “The Middle East and North Africa region is boiling with anger,” he said. “At the root of this anger is decades of neglect of people’s aspirations to realise not only civil and political rights, but also economic, social and cultural rights.”

In Cairo’s Tahrir Square, the influential Egyptian cleric Sheikh Yusef al-Qaradawi said the Arab world had changed and said Egypt’s new military leaders should listen to their people “to liberate us from the government that Mubarak formed”.

It has also emerged that the Ministry of Defence has helped train more than 100 Bahraini army officers in the past five years at Sandhurst and other top UK colleges.