The United Nations humanitarian coordinator for Syria said Thursday that the country's death toll from last week's deadly earthquake is likely to rise further as teams scramble to remove rubble in hard-hit areas.

In an interview with The Associated Press, Muhannad Hadi defended the U.N.'s response to the disaster, which many in Syria have criticized as slow and inadequate.

The U.N. has reported a death toll of about 6,000 for all of Syria, including 4,400 in the rebel-held northwest. That figure is higher than those reported by government authorities in Damascus and civil defense officials in the northwest, who have reported 1,414 and 2,274 deaths respectively.

“We’re hoping that this number will not increase by much,” Hadi said. “But from what we are seeing … the devastation of this earthquake is really not giving us a lot of hope that this will be the end of it.”

Hadi noted that even before the earthquake, there were some 4.1 million people in need of aid in northwest Syria, many of whom were already displaced and have now become homeless or displaced again.

Locals struggling with the aftermath of the earthquake have criticized delays in getting U.N. aid to the area. Roads leading to the one border crossing from Turkey to Syria that the U.N. is authorized to use were damaged by the earthquake. The first convoy of aid to enter northwest Syria came three days after the quake.

The U.N. and Syrian President Bashar al-Assad reached a deal Monday to open two additional crossings, but critics say the U.N. should have used additional crossings without waiting for approval or found another way to get aid in, in light of the dire situation on the ground.

Syrian rescue workers and those who lost homes and family members in the quake have criticized the slow arrival of aid, saying they felt abandoned by the international community.

“I can assure you that we have done everything we can from the very beginning,” Hadi said. “We asked everybody to put the interests of the people first. We asked everybody to de-politicize the humanitarian situation and focus on supporting us to reach the people.”

Hadi said 120 aid trucks had crossed into northwestern Syria from Turkey as of Thursday.

So far, no aid convoys have crossed from Damascus-controlled territory into the rebel-held areas. Hayat Tahrir al-Sham, the al-Qaida-linked rebel group that controls much of the northwest has so far refused to allow aid to cross from government areas.

Hadi said the U.N. is “working with all parties” to open the route to aid, but acknowledged that “so far, we haven’t been successful.”

The U.N. has appealed for $397 million to provide “desperately needed, life-saving relief,” including shelter, food and health care for the next three months.

More complications will almost certainly arise once the earthquake response moved from immediate emergency aid to rebuilding, but Hadi said it is too early to think about that.

“What we need to focus on right now is the humanitarian work,” he said.