A video published online by Islamic State (IS) militants claims to show Jordanian pilot Moaz al-Kasasbeh being burned alive.

The video, which could not immediately be verified, shows a man standing in a cage and engulfed in flames.

Lt Moaz al-Kasasbeh was captured when his plane came down near Raqqa, Syria, in December on a mission to support the US-led military coalition against IS.

Jordanian state TV confirmed the death and said he was killed a month ago.

The video posted online on Tuesday was distributed via a Twitter account known as a source for IS propaganda.

A relative of Lt Kasasbeh told Reuters news agency that the Jordanian armed forces had informed the family that he had been killed.

The BBC's Frank Gardner says that the video is clearly intended to shock.

The highly produced 22-minute film includes a sequence showing the Jordanian pilot walking at gunpoint amongst rubble apparently caused by coalition air strikes that targeted jihadists.

Jordan had been attempting to secure Lt Kasasbeh's release as part of a prisoner swap.

It had offered to free Sajida al-Rishawi, who is on death row in Jordan for her role in hotel bombings in Amman in 2005, in return for the release of Lt Kasasbeh.

Members of Lt Kasasbeh family had been gathering every day at a community centre not far from the royal palace in Amman.

The video emerged three days after another video appeared to show the dead body of Japanese hostage Kenji Goto.

The US state department said it was working to confirm the authenticity of the video.

US President Barack Obama said that if the video was real, it would redouble the determination of the coalition against IS to degrade and destroy it, Reuters reported.