The U.N.'s decision in July to begin moving aid into war-torn Syria without the consent of President Bashar Assad was heralded as unprecedented. It was the first time that humanitarian need trumped a nation's sovereignty.

Five months later, aid workers are dismayed that more trucks loaded with U.N. aid aren't moving into Syria, where civilians are dodging bullets and barrel bombs in the crossfire of a war that has killed 200,000. Despite their disappointment, they still want the U.N. Security Council next week to renew a resolution that permits the U.N. aid to move through four border crossings -- two in Turkey, one in Jordan and one in Iraq -- without Assad's blessing.

The U.N. humanitarian office has said that if security allowed, U.N. aid trucked through the four crossings could reach 2.9 million people, complementing the much higher levels of cross-border aid that non-governmental organizations have been moving into the country for years. So far, the number of people who have benefited from aid delivered under terms of the resolution is in the hundreds of thousands, not millions.

"While some progress has been made, over 12 million people still urgently need help," U.N. Secretary-General Ban Ki-moon wrote late last month. "Nearly 5 million of them live in areas that remain hard to reach despite the additional access granted through Resolution 2165, and only a portion are receiving humanitarian assistance."

He said the resolution had enabled U.N. agencies and partners to reach more places where assistance is urgently needed. But "needs continue to rise and the situation on the ground continues to deteriorate."

Before the resolution was adopted, the U.N. and its partners were getting aid to 38 hard-to-reach areas a month. Since its adoption, an average of 66 of these areas are reached each month.

Resolution 2165, which was approved for six months, is set to expire on Jan. 9. U.N. diplomats say they hope to vote on renewing it for a full year next week.

A half dozen aid officials and workers told The Associated Press in interviews that the cross-border U.N. aid has been slowly increasing. They say it is hampered by fighting, militant roadblocks, bureaucratic and logistical delays, poor coordination and -- in some cases -- the aid community's fear of angering the Syrian government because it needs its help with other projects in the country.

The aid workers all spoke on condition of anonymity because they said speaking publicly would make them targets for extremist militants and potentially damage their working relationships with the U.N.

One aid official, who coordinates work in several countries in the region, said that since the resolution was adopted, the U.N. had moved about 420 truckloads of aid through border crossings in Turkey and Jordan compared to the 688 truckloads of aid his organization had moved in the same time period through Turkey alone.

The aid workers said northeast Syria was especially difficult to reach because roads from warehouses are controlled by armed militant groups. They spoke of problems with the road at the Jordanian crossing but said Saudi Arabia had financed improvements. They recounted situations where aid was stolen or resold by militants or government forces, hospitals and ambulances bombed and shipments stopped before they could ever reach their destinations.

Many areas that are controlled by Islamic State militants or government forces remain impossible to penetrate or are too dangerous to visit. Sixty-nine humanitarian aid workers have been killed since 2011, including three who were beheaded by IS this year. Twenty-seven U.N. staff members are detained or missing.

Before the civil war started in March 2011, an estimated 22 million people lived in Syria. Now, nearly half are displaced -- 7.6 million have fled their homes but still live inside Syria and more than 3.2 million have become refugees in other countries.

"The Syrian crisis is the largest and most complex humanitarian crisis of our time," Nancy Lindborg, assistant administrator at the U.S. Agency for International Development, told a Senate Foreign Relations Committee panel this week. "Millions of families have been torn apart, pushed out of ancestral homes and forced to flee unspeakable horrors in search of safety and dignity.

"The Assad regime has waged a cruel and unrelenting campaign of bloodshed and starvation against its own people for almost four years."

The U.N. says parties to the conflict continue to restrict access to besieged areas. No more than two besieged areas have been reached in any month since the adoption of Resolution 2165, and only one location has been reached in each of the past two months.

The moderate Syrian National Coalition doesn't want to see the resolution just renewed. It wants to see it strengthened to make sure the Assad government faces consequences for noncompliance.

Abrahim Miro, the coalition's finance minister, said recently in Istanbul that Resolution 2165 was not solving the problem and aid still was not reaching areas held by forces fighting IS and the Assad government. He accused Assad of using humanitarian aid as a "political tool" and argued that better coordination with the opposition would allow more aid to flow into areas it holds.

"If some NGOs drop let's say 50 tons of flour in a certain city, the price of bread goes down for three days and then it goes up. This volatility is making people very tired," Miro said. "We need people to have the aid as soon as possible, and that is unfortunately not happening at the time being."