Saudi Arabia has deployed 30,000 troops to its border with Iraq after a video emerged showing 2,500 Iraqi soldiers deserting the area.
The military manoeuvre reflects growing Saudi jitters about the threat from radical Sunni insurgents to the stability of the Kingdom, despite persistent rumours that wealthy Saudi donors are channelling funds to Islamic State of Iraq and the Levant (ISIS).
The Saudi al-Arabiya TV channel reported that Saudi soldiers poured into the border region to protect the Iraqi and Syrian frontier. It also reported it had obtained a video showing thousands of Iraqi troops in the desert near the Iraqi city of Karbala, after leaving their posts on the border with the oil-rich nation.
Saudi's King Abdullah told the SPA news agency that the new security measures were being put in place to protect against terrorism.
Relations between the republic and the Kingdom, who share a 800km border, are exceptionally strained.
Saudi nationals have been accused of playing a key role as foreign fighters in the Iraq Islamist insurgency, now occupying vast swathes of the country's north and central regions, as well as northern Syria. Security officials fear many will return home radicalised further, and ready to make waves at home.
The Kingdom has denied giving any support to ISIS, which has captured swaths of territory across northern and central Iraq, as well as controlling large parts of northern Syria.
Iraqi prime minister Nouri al-Maliki claimed last month that wealthy Saudis were funding the jihadi insurgency, as well as having backed the Syrian uprising against Bashar al-Assad.
"The Kingdom of Saudi Arabia wishes to see the defeat and destruction of all al Qaeda networks and the Islamic State of Iraq and al-Sham operating in Iraq. Saudi Arabia does not provide either moral or financial support to Isis or any terrorist networks," a spokesman for the government said.
"The Saudis have made many mistakes but I don't think support for Isis has been one of them," said Shashank Joshi, of the Royal United Services Institution told the Guardian last month.
"The kingdom recognises the severity of the threat that Isis poses, particularly in the last few months. Private donations from Saudi and other Gulf states have probably been directed to Isis and those nations have generally been lax about monitoring those flows. Groups that Saudi Arabia has knowingly supported may have bled equipment, arms and funding to Isis but I don't think Riyadh had any real intention to support Isis as a counterweight to Assad or to Iran.
"They have been burned by Isis's jihadi forerunners. This is not to exculpate them for their carelessness. Maliki is trying to shift blame from himself and is echoing Iranian propaganda."
Isis's own meticulous records reveal that less than 5% of its funding has come from overseas, with most of its funding coming from ransom money, "taxation" on local citizens, and more than £244m in cash looted from banks in Iraq's second largest city of Mosul.
Nonetheless, reaching Saudi's northern border would be an intimidating prospect for any would-be insurgency. In April 2006, Saudi Arabia began construction of a border barrier along its border with Iraq, to supplement the existing 7-meter-high sand berm. There is a sophisticated system of high fences topped with barbed wire and backed by military bases.
The Syria-Iraq border, which was quite literally bulldozed by ISIS militants, presented less of a challenge, being a low sand berm that fighters drove trucks straight through.