UNITED NATIONS — Over 200,000 civilians have fled their homes in Syria around the Islamic State group’s de facto capital of Raqqa since April 1, including over 30,000 displaced just this month as U.S.-backed Syrian fighters try to oust the extremists, a senior U.N. humanitarian official said Thursday.

Assistant Secretary-General for Humanitarian Affairs Ursula Mueller told the U.N. Security Council in a video briefing from Amman, Jordan, that “an estimated 20,000 to 50,000 people remain inside Raqqa city, which is now encircled, and their situation is perilous — there is no way for them to get out.”

She also lamented that the U.N. has delivered aid to only a few hard-to-reach areas in Syria and not a single besieged location this month — and she blamed the Syrian government, armed groups, insecurity and fighting.

For those displaced in Raqqa province, she said humanitarian conditions are very difficult with temperatures now approaching 50 degrees Celsius (122 degrees Fahrenheit). The United Nations also has serious concerns over their protection, particularly over their freedom of movement outside the camps many now live in, she said.

Leaving the city of Raqqa remains “extremely difficult due to the presence of mines and other unexploded ordnance, as well as shelling, sniper activities and airstrikes,” Mueller said.

“As military operations continue, our concern is further civilian casualties,” she said, especially since Islamic State fighters have allegedly used civilians as human shields.

Mueller said the U.N. and its partners are ready to support people from Raqqa as soon as security allows it and they can gain access.

“The health situation, particularly the low availability of trauma care services, is a major concern in view of the intense fighting and shifting front lines,” she said. “We continue to engage with relevant parties and actors on the ground … but a lot more needs to be done.”

Mueller said the U.N. continues to see a reduction in violence in some areas since Russia and Iran, both supporters of Syrian President Bashar Assad, and Turkey, which backs rebels fighting Syrian government forces, agreed on a plan in May to establish four “de-escalation” zones in Syria.

But “despite reductions in violence, we have not been able to noticeably increase our reach,” she said.

Mueller said there have been no U.N. aid convoys to besieged areas in July and just one a week to hard-to-reach areas, meaning just over 120,000 people got help this month. Other U.N. partners delivered aid to some hard-to-reach areas.

In a letter to the Security Council, ambassadors from 12 Western and Arab nations and the European Union who attend weekly meetings in Geneva on humanitarian aid to Syria said they remain “extremely concerned” that the United Nations is being excluded from sending convoys to besieged and hard-to-reach areas.

“This trend has worsened significantly in recent months,” said the letter, obtained by The Associated Press. “Only two U.N. supported convoys have been able to access territory besieged by the Syrian authorities since April.”

The ambassadors urged the Security Council to underline to Syria its obligation under international law to allow humanitarian aid deliveries — and to take action given its pledge to “take further steps in the case of non-compliance.”

Britain’s U.N. Ambassador Matthew Rycroft told reporters: “We’re not asking for humanitarian access as a favor. We’re asking for it because it’s a legal and moral obligation. It’s an obligation under successive Security Council resolutions.”