"I am aware that today's strikes were not carried out at the direct request of the Syrian Government, but I note that the Government was informed beforehand," Ban Ki-moon said at the Climate Summit press conference.
The UN chief underlined that the protection of civilians should be a top priority for all parties involved in this campaign.
"As the custodian of the principles of the United Nations, I would like to underscore the importance that all measures must be fully in line with the Charter of the United Nations and need to operate strictly in accordance with international humanitarian law… The parties involved in this campaign must abide by international humanitarian law and take all necessary precautions to avoid and minimize civilian casualties," Ban Ki-moon said.
Earlier on Tuesday, Washington carried out a number of airstrikes against the IS, al-Nusra Front and Khorasan jihadist groups positions in Syria, using aircraft, drones and Tomahawk missiles. Saudi Arabia, Jordan, Bahrain, Qatar and the United Arab Emirates also reportedly took part in the attacks.
At least eight civilians, including three children, were killed in the strikes, according to Syrian Observatory for Human Rights.
Obama unveiled a strategy for defeating the IS on September 10. The plan includes forming an international coalition to fight the radical organization and authorizing US airstrikes against IS targets in Syria, while simultaneously continuing airstrikes in Iraq, which the United States authorized in August.
The IS, also known as the Islamic State of Iraq and Greater Syria (ISIS), has been fighting against Syrian government since 2012. In June 2014, the group extended its attacks to northern and western Iraq. Ceasing vast territories in both countries and forcing thousands of people, mostly religious minorities, to flee, the IS declared a caliphate on all the territories under its control.