The United Arab Emirates has suspended its air attacks against the Islamic State in Syria since the capture of a Jordanian pilot who was burned alive by the jihadi group, it has emerged.

US officials confirmed that the UAE, one of the four Arab states in the anti-Isis coalition, had ceased its participation because of concerns over a lack of contingency plans to rescue downed aircrew.

The news came as Jordan pledged to strike back hard at Isis over the brutal murder of the pilot, Muadh al-Kasasbeh, but against a background of concern that after an initial backlash to satisfy calls for revenge, popular opposition to the campaign may grow in the kingdom.

Jordan said there would be an “earth-shattering response” – even before the hanging of two al-Qaida prisoners on Wednesday.

The UAE, Jordan, Saudi Arabia and Bahrain joined the coalition when attacks began in September. All have flown sorties against Isis targets, but in the absence of any statistics in US military communiques and silence in their own capitals, most observers believe their participation has been largely symbolic.

President Barack Obama was keen to have Sunni Arab support to avoid the impression that the US alone was fighting the jihadi group. But critics, in Jordan and elsewhere, still attack the operation as an “American war” that is doing little to turn the tide against President Bashar al-Assad’s regime in Syria.

The New York Times reported that the UAE, shocked by Kasasbeh’s capture, is demanding that the Pentagon improve its search-and-rescue efforts, including the use of V-22 Osprey tilt-rotor aircraft, in northern Iraq, closer to the battleground, instead of basing the missions in Kuwait. The country’s pilots will not rejoin the fight until the Ospreys are put in place in northern Iraq, the paper said.

UAE officials have also reportedly expressed concern to the US that Iran is playing too large a part in the war against Isis. They especially dislike the prominent role being played by Iranian-backed Shia militias in Iraq, where anti-Sunni sectarianism is rife. Saudi Arabia, Iran’s greatest regional rival, shares those concerns.

The irony is that when the anti-Isis campaign began, the Emiratis were keen to advertise their participation, showcasing a female F16 pilot who flew one of the first sorties in Syria. The Saudis did the same with a pilot who was a member of the royal family. The Jordanians, by contrast, have maintained a lower profile, largely because of domestic criticism of King Abdullah’s decision to take part.

Shaikh Abdullah Bin Zayed Al Nahyan, the UAE foreign minister, condemned Kasasbeh’s murder. “This heinous crime represents a brutal escalation by [the] Daesh [Isis] terrorist group and revealed its evil goals,” he said.

Jordan hanged a jailed Iraqi militant whose release had been demanded by Isis before it burned Kasasbeh to death.

The Jordanian authorities also executed another senior al-Qaida prisoner sentenced to death for plots to wage attacks against the pro-western kingdom in the past decade.

Sajida al-Rishawi, the Iraqi female militant, was sentenced to death for her role in a 2005 suicide bomb attack that killed 60 people. Ziyad Karboli, an Iraqi al-Qaida operative who had been convicted in 2008 for killing a Jordanian, was also executed at dawn.

The executions were confirmed by government spokesman Mohammed al-Momani. The prisoners were executed in Swaqa prison, a large facility 70km (45 miles) south of the capital, Amman, just before dawn, a security source who was familiar with the case told Reuters. The executions of three other convicted terrorists were also scheduled for Wednesday.