An al-Qaeda-linked group fighting in Syria has released video of the first American to carry out a suicide attack in the country's civil war, showing him smiling and saying he looked forward to going to heaven.

Al-Nusra Front released the new video on Friday showing American citizen Moner Mohammad Abu-Salha, 22, with other fighters before the May 25 attack that targeted several army positions in the government-held city of Idlib in northwestern Syria.

It said two of the other three suicide attackers were from foreign countries, including one who was identified as being from the Maldives.

Abu-Salha appears smiling in the video and speaks in broken Arabic.

"I want to rest in the afterlife, in heaven. There is nothing here and the heart is not resting," Abu-Salha says.

"Heaven is better. When people die they either go to heaven or hell. There is happiness beyond explanation.''

The video, released by al-Nusra Front's media arm, al-Manara al-Baydha, was posted on self-proclaimed jihadi websites.

It corresponded with Associated Press reporting about the attack and Abu-Salha. Al Jazeera cannot confirm the authenticity of the video due to reporting restrictions in Syria.

Opposition forces previously identified the American who carried out the bombing as Abu Hurayra al-Amriki and said he was a US citizen. The name al-Amriki means "the American'' in Arabic.

It is not known how many people were killed in the bombing.

Fighters belonging to al-Nusra Front said Abu-Salha's lorry was laden with 16 tonnes of explosives to tear down the Fanar restaurant, a gathering site for Syrian troops.

Other suicide attackers targeted nearby army positions.

Abu-Salha grew up in Florida and attended several colleges before dropping out and moving abroad.

Thousands of foreign fighters have come to Syria from around the world to fight against President Bashar al-Assad's forces after the uprising against his government began three years ago.

In May, James Comey, the FBI director, said dozens of Americans were joining Syria's civil war.

Gas field recaptured

In other Syria-related developments, the Syrian Observatory for Human Rights said Syrian troops recaptured the Shaer gas field in the central province of Homs a week after fighters from the Islamic State group captured it and killed dozens of soldiers.

Syrian state television confirmed that troops recaptured the field, saying that "large numbers of Islamic State terrorists were wiped out".

The Britain-based Syrian Observatory also reported on Saturday that the number of soldiers killed over the past few days in a northern military base in Raqqa that was overrun by the Islamic State group had risen to 85.

It said the fate of 200 other soldiers was still unknown.

The Syrian Observatory said Islamic State fighters had executed and paraded the bodies of "tens'' of soldiers in Raqqa, the only provincial capital in rebel hands.

Amateur videos posted online by activists showed more than a dozen beheaded bodies in a busy square said to be in Raqqa. Some of the heads were placed on a nearby fence, where at least two headless bodies were crucified.

The war, which began in 2011, has since taken on strong sectarian overtones, pitting a Sunni-led insurgency that includes al-Qaeda-inspired groups against a government dominated by Assad's minority Alawite sect, an offshoot of the Shia sect.

Syria's uprising began with peaceful protests in March 2011 but escalated into an armed revolt when government forces launched a sweeping crackdown on dissent.

The conflict has killed at least 170,000 people, nearly a third of them civilians, according to activists. Nearly three million Syrians have fled the country.