* "A change in their approach"
* More than 2 million believed to be internally displaced
WASHINGTON, Feb 6 (Reuters) - Syrian President Bashar al-Assad may have allowed humanitarian aid into previously inaccessible rebel-held parts of Syria to try to win the loyalty of the residents, a senior U.S. official said on Wednesday.
The Office of the United Nations High Commissioner for Refugees, the U.N. refugee agency, said on Friday it had reached an opposition-held area of north Syria for the first time and found about 45,000 displaced people in appalling conditions.
The Syrian government agreed to give the United Nations access to the zone of Azaz, north of Aleppo near the Turkish border, enabling a convoy to deliver tents and blankets to needy people living in the open in freezing temperatures.
More than 2 million people are estimated to be internally displaced within Syria and more than 700,000 refugees have fled to neighboring countries due to the nearly two-year conflict between Assad and rebels seeking to overthrow him.
"We think that one thing they (the Syrian authorities) may have calculated is that they ought to pacify some of the country by making sure that aid got through," Anne Richard, the U.S. assistant secretary of state for population, refugees and migration, said in a conference call.
"So there has been a change in their approach, but it's hard to speculate what's really motivating them," she added, saying she had asked U.N. officials, "and that was the only answer I had heard, was that they perhaps wanted to keep some of the people in the countryside loyal to them."
Separately, an International Committee of the Red Cross, or ICRC, official said the group had recently been able to deliver aid with the government's consent to other opposition-held parts of Syria, including Houla in Homs province.
"The reason why this area is interesting is that it is opposition-held, and it has been sealed off for three months, where potentially no or very, very little humanitarian aid has entered into this area," Andres Kruesi, deputy head of the ICRC delegation in Syria, said in an interview posted on the Geneva-based aid agency's site on Wednesday.
Kruesi said the ICRC and volunteers from the Homs branch of the Syrian Arab Red Crescent had delivered mostly food aid and hoped to make a second delivery of food and medical supplies next week.
'HAVE TO REPLICATE THIS'
"It was quite a success that we have gained this access last week and we have done so with the consent of all parties involved," he added, saying that included the various security services on the Syrian government side and representatives of the armed opposition.
Kruesi said the ICRC also was able to enter Tall Kalakh, which he described as a small city on the border with Lebanon that was one of the early hot spots of the conflict and where he said most houses were riddled with bullet holes.
"But over the last weeks now, there has been a local accommodation, negotiated at the government level, where the armed opposition and government have agreed on a ceasefire, which we now try to follow up with humanitarian aid," he said.
"So the challenge over the next weeks will be to follow up on this field trip and to gain access to similar areas like ... Houla that are encircled, to negotiate with a multiplicity of stakeholders," he said. "We have to replicate this in other governorates (provinces), including also in rural Damascus."
The U.N. Office for the Coordination of Humanitarian Affairs estimated on Jan. 17 that 4 million people were in need of humanitarian assistance across all 14 governorates in Syria. Of those, 3 million lacked food and 2 million were displaced. (Reporting By Arshad Mohammed; Additional reporting by Stephanie Nebehay in Geneva; Editing by Peter Cooney)