Air strikes in eastern Syria killed 26 Iraqi fighters from an Iran-backed paramilitary force after a deadly attack on US-led coalition forces in Iraq, a monitoring group has said.

The Syrian Observatory for Human Rights said Popular Mobilisation camps near the border town of Albu Kamal were hit.

It was not clear who carried out the strikes. The coalition did not comment.

But it followed a rocket attack on the Taji military base in Iraq that killed a British soldier and two Americans.

Another 12 coalition service personnel were injured by the 18 Katyusha rockets that were launched from a lorry later discovered a few kilometres from the base.

UK Prime Minister Boris Johnson called the attack on the base “deplorable”, while US Secretary of State Mike Pompeo said those responsible would be held accountable.

No-one claimed they launched the rockets, but the US has accused Iran-backed militias of 13 similar attacks on Iraqi bases hosting coalition forces in the past year.

The killing of an American civilian in one such incident in December triggered a round of violence which ultimately led US President Donald Trump to order the assassination of the top Iranian general Qasem Soleimani while he was meeting the deputy commander of the Popular Mobilisation in Baghdad the following month.

A retaliatory Iranian ballistic missile strike on an Iraqi air base left more than 100 US troops suffering from traumatic brain injuries (TBI).