Mekdad's remarks came a day after the Syrian army denied media reports that the US air force struck positions of the Islamist militants in Syria's al-Raqqa province, which has largely fallen to the Islamist fighters.
Syria has long accused the US of supporting terrorism in the region and has maintained that the bloody civil war engulfing the country is a war on terrorist groups aiming to destabilise the country.
Washington is aiding the Kurds in Iraq against the Islamic State, an Al Qaeda break-away group, in the country's north, backing them up with air strikes on Islamic State positions.
On Monday, media reports said that the Kurdish militias succeeded in recapturing the Musel Dam from the insurgents with the help of the US air force.
The Islamic State, previously known as the Islamic State in Iraq and the Levant, has recently proclaimed it established an " Islamic Caliphate" in parts of Syria and Iraq, threatening the political geography of the region.
The group led by Abu Bakr al-Baghdadi, who is said to have command over tens of thousands of fighters, said their goal is to establish an Islamic state in Iraq and Syria to fight the Shiite- led Iraqi central government and Syrian President Bashar al-Assad, whose top ranks are from the Alawite minority, an off-shoot of Shiite Islam.