UNITED NATIONS, Aug. 21 (Xinhua) -- Three more civilians reportedly have been killed and 14 others wounded -- including two children -- in stepped-up clashes in northwestern Syria, a UN spokesman said on Wednesday.

Stephane Dujarric, spokesman for UN Secretary-General Antonio Guterres, said humanitarian colleagues reported the latest casualties taking place Tuesday in Idlib governorate.

More than 500 civilians had been killed in clashes in northwestern Syria since the end of April, Dujarric said earlier.

Between May 1 and Aug. 18, 576,000 movements by displaced people have been recorded in the northwest of the country, the spokesman said. Many people have been displaced up to five times, with some having been forced to move as many as 10 times due to the ongoing fighting.

Tuesday alone, about 1,500 people living in northern Hama governorate reportedly were uprooted to move further northwards into Idlib governorate, he said.

The secretary-general said on Tuesday he was deeply troubled by the continued escalation of fighting in northwestern Syria and the prospect of an offensive deeper into Idlib, which could trigger a new wave of human suffering possibly impacting more than 3 million people, the spokesman said.

"He strongly condemns continued attacks on civilians and civilian infrastructure, including on healthcare and educational facilities," Dujarric said. "He urges all parties to respect fully international humanitarian law."

The secretary-general reiterated his urgent call for the September 2018 Memorandum of Understanding (MOU) on Idlib to be upheld, the spokesman said. He also stressed the importance of advancing the UN-facilitated political process in Geneva, mandated by the Security Council.

The MOU reached in September 2018 between Russia and Turkey called for de-escalation in the northwest of Syria in order to protect civilians in the region from advancing forces supporting the Syrian government.