This image made from undated video posted during the weekend of June 28, 2014 on a social media account frequently used for communications by the Islamic State of Iraq and the Levant (ISIL), which has been verified and is consistent with other AP reporting, shows Omar al-Shishani standing next to the group's spokesman among a group of fighters as they declare the elimination of the border between Iraq and Syria. AP Photo/militant social media account via AP video Saudi Arabia is calling on its allies, Egypt and Pakistan, to provide military assistance in keeping its border closed to militants that have already taken over vast swaths of Iraq and Syria, The London Times reports.

"The kingdom is calling in favors from Egypt and Pakistan," an adviser to the Saudi government told The Times. "No one is certain what ISIS has planned, but it’s clear a group like this will target Mecca if it can. We expect them to run out of steam, but no one is taking any chances."

The formerly al Qaeda-aligned group, Islamic State of Iraq and the Levant (ISIS), has taken over a number of key cities in Iraq in recent months, after previously carving out territory in Syria.

The Saudi government has reason to worry. It has been covertly supplying cash and weapons, along with Qatar, to rebels fighting Syrian President Bashar al-Assad. "ISIS has been a Saudi project," a senior Qatari official told Steve Clemons of The Atlantic.

The reason for Saudi Arabia's support of rebel groups is in opposition to Iran, which backs al-Assad. But now it appears — much like U.S. support in the 1980s for mujahideen fighters in Afghanistan — that decision may come back to bite them.

A large-scale ISIS incursion into Saudi Arabia seems unlikely, but the threat of battle-hardened fighters making their way into the kingdom to attack from inside is very real. In some cases they already have, as the Saudi Interior Ministry reported in May it had discovered an ISIS cell of 62 members inside the country, most of them Saudis, according to Al Monitor.

Saudi Arabia has been fighting terror groups for many years, and even had a bloody siege in 1979 between government forces and militants inside Mecca's Grand Mosque, one of the holiest sites in Islam.

In the standoff, the Mosque's minarets were destroyed, while other parts were peppered with grenade shrapnel and bullets in fighting that lasted two weeks, according to the book "Inside the Kingdom" by Robert Lacey.

"No one has taken any initiative to root these guys out," Theodore Karasik, of the Institute for Near East and Gulf Military Analysis in Dubai, told the Times. "Once they have consolidated, there is a danger they will try to go back into the kingdom."