The United Nations says the number of refugees who have fled Syria has reached more than 250,000, calling the humanitarian problems sparked by the conflict “our biggest crisis.”

The U.N. refugee agency said Tuesday there are more than 85,000 Syrians registered in Jordan, nearly 78,500 in Turkey, 67,000 in Lebanon and 22,500 in Iraq.

Agency spokeswoman Sybella Wilkes told VOA the numbers are increasing “by the thousands every day.” She said UNHCR's two main priorities are for neighboring countries to keep their borders open and for a “dramatic increase” in international support to facilitate the effective accommodation of refugees.

Wilkes described the conditions in Jordanian refugee camps – where 27,000 Syrians are sheltering in tents – as “unacceptable.” She warned that the searing heat of summer will soon give way to harsh winter weather.

Special UNHCR envoy, actress Angelina Jolie, is touring Jordan's Zaatari refugee camp along with U.N. refugee chief Antonio Guterres and Jordanian Foreign Minister Nasser Judeh.

Also Tuesday, activists said Syrian troops pounded the northern city of Aleppo to thwart a rebel advance. Violence and bloodshed were reported in other parts of Syria as peace envoy Lakhdar Brahimi was set to meet members of the Syrian opposition in Cairo ahead of a planned visit to Damascus for talks with government officials.

British Foreign Secretary William Hague was also in Cairo for talks with President Mohamed Morsi on Syria, amid heightened diplomacy in the Egyptian capital where Syrian neighbors also gathered to discuss the conflict.

The first meeting of a regional contact group took place late Monday in Cairo with delegations from Egypt, Turkey, Iran and Saudi Arabia gathering to discuss the deteriorating situation in Syria.