Saudi King warns of terrorist threat to Europe, US

King Abdullah of Saudi Arabia has told ambassadors militants pose a threat and "after a month they will reach Europe and, after another month, America".

Saudi King Abdullah bin Abdulaziz al-Saud speaks before a meeting with the US Secretary of State at his private residence on June 27, 2014 in the Red Sea city of Jeddah. (File: AAP)

The king of Saudi Arabia has warned that terrorist groups will attack Europe and the United States unless they are faced with collective "power and speed" from the international community.

King Abdullah's comments come as the Islamic State group has seized wide swaths of land across Syria and Iraq.

While not mentioning any terrorist groups by name, Abdullah said that he is "certain that after a month they will reach Europe and, after another month, America".

The king's comments late on Friday appeared aimed at drawing US and NATO forces into a wider fight against extremists in the region.

Saudi Arabia has backed rebels fighting in Syria, but is concerned that extremists there could turn their weapons on the kingdom.

State media carried the king's comments to foreign ambassadors early on Saturday.