West will be next ISIS target unless there is 'rapid' action, Saudi King warns, as jihadists now behead a Lebanese soldier

The king of Saudi Arabia has warned that Europe and the U.S. could be ISIS's next targets unless Western government fight terrorism with 'force, reason and speed'.

King Abdullah said extremists 'know no border' and could begin sweeping through countries outside of the Middle East unless action is taken.

His comments, made at a reception for foreign ambassadors, came as ISIS posted another video on social media showing the beheading of a Lebanese soldier who was captured in Syria. 

Although he did not mention any terrorist groups by name, King Abdullah's comments - published by state media today - appeared to be aimed at drawing Washington and NATO forces into a wider fight against the Islamic State and its supporters in the region.

The group has already seized wide areas of land across Syria and Iraq. 

He said: 'If we ignore them, I am certain that after a month they will reach Europe and, after another month, America.

'These terrorists do not know the name of humanity and you have witnessed them severing heads and giving them to children to walk with in the street.'

British officials raised the country's terror threat level Friday to 'severe', its second-highest level, because of developments in Iraq and Syria.

The White House has said it does not expect the U.S. to bump up its terrorism threat warning level. 

He continued: 'Terrorism knows no border and its danger could affect several countries outside the Middle East.

'It is no secret to you, what they have done and what they have yet to do. I ask you to transmit this message to your leaders: "Fight terrorism with force, reason and speed".' 

While providing arms and support to Sunni militants in Syria, Saudi Arabia has denied directly funding or backing the Islamic State group. 

Islamic State, which declared a 'caliphate' in June in parts of Iraq and Syria under its control, has been cited as a major security threat by Western governments since posting a video in August of the beheading of U.S journalist James Foley. 

The group has been fighting moderate rebels, other extremists and Assad's forces in Syria for nearly three years.