Iraq crisis
A fighter of the Islamic State of Iraq and the Levant (Isis) holds an Isis flag and a weapon on a street in the city of Mosul.Reuters

Saudi Arabia's King Abdullah has ordered "all necessary measures" to be implemented to protect his country from the Islamic State of Iraq and the Levant (Isis) as the group reaches the shared border with Iraq.

The state-run SPA news agency said that Saudi troops had been placed on high alert to ensure the security and stability of the country in the face of terrorist threats.

"Anticipating (that) the terrorist organisations or others might carry out actions that might disturb the security of the homeland, the Custodian of the Two Holy Mosques has ordered taking all necessary measures to protect the gains of the homeland and its territories in addition to the security and stability of the Saudi people."

Fear has grown since the terrorist group's capture of border posts on the Jordanian border, which Saudi Arabia also neighbours. Saudi intelligence has discovered that Isis militants have been heading towards the Saudi border with the aim of seizing the strategic border crossing of Ar Ar.

A Saudi Arabian official, speaking on condition of anonymity, confirmed to CNN that security forces had been placed on the highest level of alert.

"Saudi Arabia shares a long border with Iraq and the government is aware that Isis is very close to Iraq's border with Jordan, and is also aware Isis has been very public about its intention to attempt to attack Saudi Arabia," the official said.

The unnamed official also spoke of the multi-dimensional threat facing Saudi Arabia with members of al-Qaida in the Arabian Peninsula (AQAP) militants attempting to enter the country from Yemen.

"While Saudi security forces are at the ready and very strong, the threat emanating from Yemen is still very real," said the official.