A Republican senator and surrogate for Mitt Romney chided the GOP presidential nominee on Wednesday, saying he was "a bit dismayed" by Romney's foreign policy speech earlier in the week.

In an op-ed on CNN.com, Sen. Rand Paul of Kentucky, who endorsed Romney in June, took issue with key points of Romney's approach to international affairs.

"Romney chose to criticize President Obama for seeking to cut a bloated Defense Department and for not being bellicose enough in the Middle East, two assertions with which I cannot agree," Paul wrote.

A tea party favorite and known for his libertarian views--many of which he shares with his father and former presidential candidate Ron Paul--Sen. Paul maintained he's not an isolationist, as he believes in engagement with the world through trade, commerce and diplomacy. He would not hesitate, he added, to send troops to war as a measure of self-defense.

"But we are in too many places, too often, and we don't seem to even know the reason - or where we will end up when we're done," he wrote. "This foreign policy has created more enemies than it has vanquished."

Paul pointed to Romney's speech Monday, in which the Republican candidate outlined his foreign policy visions for several countries in the Middle East. Regarding the ongoing unrest in Syria, he said would work with other countries to ensure that certain members of the opposition "obtain the arms they need to defeat" Bashar al-Assad's regime. He also proposed how he would urge and work with governments in the Middle East and North Africa to strengthen Democratic institutions.

Paul, however, wrote that such policy exemplifies how both parties "rush headlong into more places they don't understand." Instead, he wrote that the right response is "to step back and think of whether we really need to be involved in these countries in the way we have been."

The Kentucky senator, elected in 2010, also hit back at Romney's call for a stronger military, saying the growth of defense and war spending has grown at a rate that is unsustainable.

"If debt is our gravest threat, adding to the debt by expanding military spending further threatens our national security," he said.

Paul campaigned for Romney as recently as late September, when he appeared in Ohio with the GOP nominee, his running mate, Rep. Paul Ryan, and Sen. Rob Portman. In his op-ed, he said that he would continue to stump for Romney this week.

Romney isn't the only target of Paul's frustration this week. The freshman senator made headlines when he took out television ads against two Democratic senators running for re-election, Bill Nelson of Florida and Joe Manchin of West Virginia. Paul spent six figures in both states railing against the lawmakers for voting to send foreign aid to Libya, Egypt and Pakistan.