UNITED NATIONS, July 29 (Xinhua) -- Close to 500 civilians have been killed in the violence in Syria since April 28, and more than 440,000 people have been displaced, a United Nations spokesman said on Monday.

"Our humanitarian colleagues remain deeply concerned for the safety and protection of civilians in northwest Syria, where some 3 million women, children and men remain caught in the crossfire," Farhan Haq, deputy spokesman for UN Secretary-General Antonio Guterres, said at the daily news briefing.

This weekend alone, at least 35 people, including three health workers, were reportedly killed in a succession of airstrikes and shelling on densely populated urban areas in territory controlled by non-state armed groups, said Haq.

"Shelling also reportedly affected urban areas in government-controlled zones," he added.

Referring to other destructions, the spokesman said that "extensive damage" to residential areas and civilian infrastructure reportedly included seven schools, a health clinic, a market, and a bakery.

"Thousands of people fled towards the Turkish border this weekend as well," he noted.

"The UN reminds all parties to the conflict, and those who have influence over them, of their obligation to protect civilians and civilian infrastructure, and of the principles of distinction and proportionality enshrined in International Humanitarian Law," said Haq.