Saudi Arabia has "a great deal of explaining to do" on how it could not defend its "most critical" oil facility from drone attacks at the weekend, said Gary Grappo, former U.S. ambassador to Oman. The Kingdom spent an estimated $67.6 billion on arms in 2018, according to Stockholm International Peace Research Institute. Saudi Arabia was just behind the U.S. and China in terms of defense spending, Grappo told CNBC's "Squawk Box" on Tuesday. "I think the Saudi leadership has a great deal of explaining to do that a country that ranks third in terms of total defense spending ... was not able to defend its most critical, and I can't underscore that enough, its most critical oil facility from these kinds of attacks," said Grappo, who was previously in senior positions at the U.S. embassies in Riyadh, Saudi Arabia, and Baghdad, Iraq. Saudi Arabia is one of the world's largest oil exporters, and damage to its oil facilities ignited fears of supply disruption around the world.

It's a bit alarming that these folks got through ... they were exquisitely precise, they knew exactly what to hit, they hit it perfectly. Bob McNally Rapidan Energy Group

Oil prices jumped after the Saturday attack on Saudi Aramco's oil processing facility at Abqaiq and the nearby Khurais oil field. That knocked out 5.7 million barrels of daily crude oil production — which is more than half of Saudi Arabia's global daily exports and over 5% of the world's daily crude production. The U.S. and Saudi Arabia have blamed Iran for the attacks.