Updated

The U.N.'s humanitarian chief sharply criticized the Syrian government's lack of progress in allowing desperately needed aid to people in Syria, telling the Security Council Friday that the regime's delays in withholding cross-border aid deliveries "arbitrary and unjustified."

Valerie Amos gave her first such report since the council last month approved a resolution demanding both the government and the opposition allow immediate access everywhere in the war-ravaged country to deliver aid.

Council members said they will in the coming days and weeks discuss the "further steps" that the resolution threatens if its requirements are not met.

Samantha Power, the U.S. ambassador to the U.N., called the briefing "harrowing" and said the Syrian government has "utterly failed to comply" with the resolution.

While Syria's ambassador said much has been "achieved" in the month since the resolution, current council president Sylvie Lucas, the Luxembourg ambassador, said, "On the contrary, the situation has only continued to worsen."

The conflict in Syria is now in its fourth year, with no end in sight. Amos said the violence has "intensified over the past four weeks."

Secretary-General Ban Ki-moon has said 3.5 million people are estimated to need aid in hard-to-reach areas in Syria, an increase of 1 million since the beginning of the year. Overall, more than 9.3 million people in Syria are in need of humanitarian aid, including 6.5 million internally displaced, Ban said.

The Security Council resolution demands that all parties, especially the Syrian government, promptly allow safe access for humanitarian aid across conflict lines and borders, and it calls on both sides to immediately lift sieges of populated areas. It also demands that all parties stop depriving civilians of food, halt attacks against civilians and demands that all foreign fighters withdraw from Syria.

Amos said the "piecemeal approach" to delivering aid is not enough, and she said the situation will continue to be bleak without "full and unhindered access" to the people in need. Spending days and weeks on approving a single convoy is "a waste of valuable time," she said.

Britain's ambassador, Mark Lyall Grant, pointed out that about 220,000 people remain under siege, with only about 14,000 people reached with aid in the past month.

Amos also called the Syrian government's use of barrel bombs "a flagrant violation of international law."

Syria's ambassador, Bashar Ja'afari, denied the use of the bombs, saying, "No. What you see on TV is publicity. ... We are not killing our own people."

The Syrian government recently approved the opening of one border crossing with Turkey, but council members appealed for more open crossing along that border, which they said would allow aid to reach an estimated 3.35 million people.

Power blamed the Syrian government alone for denying the U.N. access to the other crossings, which are held by rebels.

U.N. agencies generally do not cross borders without government permission, even if a government isn't in control of a certain area or crossing.