REYHANLI, Turkey (Reuters) - Relief operations to meet the needs of nearly 1 million people who fled recent fighting in northwest Syria’s Idlib have been overwhelmed, the U.N. aid chief said on Tuesday as the United States and Britain pledged to step up aid efforts.

While Syrian government forces fought Turkey-backed rebels in Idlib, U.S. and U.N. officials visited Turkey’s Hatay border province to view efforts to cope with one of the biggest humanitarian crises of Syria’s nine-year civil war.

The heads of the U.N. World Food Program (WFP) and the U.N. Children’s Fund UNICEF also both posted photos on Twitter of them visiting families in an area of rural Idlib on Tuesday, described as being 30km (19 miles) from conflict front lines.

The United Nations is scaling up assistance after agreeing with Turkish authorities to double the number of trucks it sends across the border to 100 each day, said Mark Lowcock, U.N. Under-secretary General for Humanitarian Affairs.

“This relief operation has been overwhelmed. There needs to be more of everything. The first thing is money,” Lowcock told reporters at a trans-shipment point for U.N. supplies in Turkey’s Reyhanli district.

The number of displaced people has surged to 980,000, more than half of them children, who are now coping with inadequate shelter and a lack of sanitation facilities in areas near the Turkish border, he said.

Lowcock said $1 billion was needed annually to sustain relief operations for a couple of million people in the Idlib region, noting there were not enough tents.

Kelly Craft, U.S. Ambassador to the United Nations who was also inspecting the relief efforts, announced $108 million additional funding for the operations.

“Humanitarian aid is only a response but the solution is an immediate ceasefire,” Craft told reporters. “We are asking for other countries to step up and contribute.”

Britain’s Foreign Minister Dominic Raab said during a visit to Ankara that his country was giving an additional 89 million pounds ($114 million) in aid to Syria, part of it to Idlib.

Fighting in Idlib has escalated in recent days as Turkey steps up military operations to counter advances by Syrian government forces, backed by Russia, in the last remaining bastion held by rebels in the country’s northwest.

“This is not something that just happened. This is planned by the Assad regime,” Craft said. “It is cruel and brutal.”

Turkey, which has sent thousands of troops and military hardware into Idlib to confront Syrian President Bashar al-Assad’s forces, hosts 3.6 million Syrians and has closed its border saying it cannot take in more migrants.

Ankara said last week it would no longer uphold a 2016 accord with the European Union to keep refugees on its territory in return for aid, leading to thousands of migrants seeking to breach the border into Greece.

($1 = 0.7826 pounds)