Washington, Sep 3 (IANS) Just two weeks after beheading American photojournalist James Foley, the Islamic State (IS) Sunni extremist organisation sent what it called "a second message to America", with a video showing the beheading of another kidnapped American journalist.

In the video released Tuesday Steven Sotloff, 31, a freelance journalist who was captured in northern Syria a year ago, speaks to the camera before he is killed.

Sotloff says is "paying the price" for US decision to strike IS targets in Iraq, CNN reported.

The masked IS figure in the video speaks to the US President Barack Obama, telling him, "Just as your missiles continue to strike our people, our knife will continue to strike the necks of your people."

The video also threatens the life of British captive, David Haines. At least two other Americans are believed to be held by IS militants.

As the videotaped beheadings and threats by IS plunged the Obama administration into a major crisis, the White House press secretary, Josh Earnest, said that the Obama administration would work to confirm the authenticity of the video.

State Department spokesperson Jen Psaki told reporters that American intelligence agencies would "work as quickly as possible" to determine whether the video was authentic.

She said the US would be "sickened" by confirmation of Sotloff's beheading.

Citing the SITE Intelligence Group, a research organisation that tracks jihadis web postings, the New York Times said the video shows the same masked fighter with British-accented English who appeared in the video of Foley's beheading.

"I am back, Obama, and I am back because of your arrogant foreign policy towards the Islamic State," says the masked executioner.

Times said it was unclear from the video of Sotloff, as where and when it was recorded.

The video reported by SITE Tuesday showed Sotloff with a small beard and some hair on his head in contrast to the Aug 19 video showing Foley's death, in which Sotloff was nearly bald and relatively clean shaven.

This indicated that the video was probably made at different times, the Times said.

Last week, Sotloff's mother Shirley Sotloff released a video pleading with IS leader Abu Bakr al-Baghdadi not to kill her son.

"Steven is a journalist who travelled to the Middle East to cover the suffering of Muslims at the hands of tyrants. Steven is a loyal and generous son, brother and grandson," she said.

"He is an honourable man and has always tried to help the weak."