The official, who spoke on condition of anonymity, criticized the Russian air strikes near al-Tanf and said no Russia or Syrian ground forces were in the area at the time.
“Russia’s latest actions raise serious concern about Russian intentions,” the official said.
“We will seek an explanation from Russia on why it took this action and assurances this will not happen again.”
In a related development a British-based monitoring group said warplanes had struck a meeting of U.S.-backed forces fighting against Islamic State in al-Tanf village killing two fighters and wounding four others.
The group known as the Syrian Observatory for Human Rights said it was unclear whose planes had carried out the attack, however.
Washington has consistently refused to join forces with Russia in Syria against Islamic State ever since Moscow launched its campaign of air strikes in September last year.
It accused Moscow of acting solely to prop up Syrian President Bashar al-Assad.
The U.S. has called on Assad to step down. (Reuters/NAN)