The council said it was 'gravely concerned at the lack of effective implementation of its resolutions'
The UN Security Council on Tuesday renewed a resolution facilitating the cross-border delivery of aid to millions of Syrians, while complaining previous such measures were not seen through on the ground.
The text was adopted unanimously by the 15 member states, which include Syrian ally Russia.
The resolution extends authorisation for UN humanitarian convoys to cross into Syria without the consent of the Damascus government, in line with a previous text adopted in July 2014 and due to expire in January.
Since last year trucks have passed through rebel-held areas from Turkey, Jordan and Iraq.
The document said the Security Council was "gravely concerned at the lack of effective implementation of its resolutions" calling for greater facilitation of aid deliveries.
It also expressed "further grave concern at the continuing and growing impediments to the delivery of humanitarian assistance across conflict lines, including through a decline in convoy approvals by the Syrian authorities".
Between 2013 and 2015, it said, the percentage of convoys approved by Syrian authorities declined from 65 percent to 29 percent.
The council also said that the Islamic State (IS), al-Nusra Front and other hardline groups had hindered aid deliveries "through deliberate interference and obstruction".
In all, some 4.2 million Syrians have fled the country while 4.5 million remain in "hard-to-reach areas," the Security Council said.
A total of 393,700 civilians are trapped in even worse-off "besieged areas," it said, warning that "the situation will continue to deteriorate further in the absence of a political solution to the Syrian conflict."
The council added that some 6.5 million have fled their homes, and 4.5 million people - including Palestinian refugees - are living in areas that are difficult to reach.