A top U.N. aid official says the Islamic State group is taking violence against civilians in Syria "to a new level" and is threatening the cross-border humanitarian aid operations recently approved by the Security Council.

The U.N.'s deputy humanitarian chief, Kyung-wha Kang, told the council on Thursday that both the extremists and the al-Qaida-linked Nusra Front are advancing on the border crossings with Turkey of Bab al-Salam and Bab al-Hawa "and could hinder additional cross-border operations."

The threat comes as U.N. humanitarian officials reported the first bit of improvement on getting aid to hard-to-reach people inside Syria, where more than 190,000 people have been killed in the conflict and almost one in two Syrians is either internally displaced or a refugee.

Kang says the death toll is likely "much higher."