* Visas denied for US, Canadian, British, French - U.N.
* Fighting prevents aid workers from reaching many in need
* Syrian wheat harvest falls, according to UN survey
* U.S. says sick, wounded face abuse by "regime forces" (Adds details, quotes by EU, U.S. officials)
By Stephanie Nebehay
GENEVA, July 16 (Reuters) - Syria is refusing visas to Western aid workers, hampering United Nations efforts to expand further its humanitarian operation to meet growing needs in the conflict-torn country, a senior U.N. aid official said on Monday.
Some 1.5 million people require assistance in Syria amid escalating violence and "political failure" to resolve the crisis, John Ging told reporters in Geneva.
Insecurity remains a tremendous challenge as fighting prevents aid agencies from reaching increasingly hungry and desperate civilians in flashpoint areas including Homs, he said.
"We have a number of visas pending for international staff from a number of Western countries - the United States, Canada, the UK, France and one or two more - that are refused their visas because of their nationalities," said Ging, of the U.N. Office for the Coordination of Humanitarian Affairs.
"That is something we object to very strongly and are working with the Syrian government to overcome," he said after chairing the Fourth Syrian Humanitarian Forum in Geneva.
The world body now deploys some 60 expatriate staff in Syria, where U.N. officials were taking up the key issue of blocked visas "on a daily basis" with Damascus, he said.
Otherwise, Syria is largely respecting an agreement reached in June, he said. The U.N. has opened offices in 7 locations and is delivering aid mainly via the Syrian Arab Red Crescent and others to people in all 14 provinces affected by the conflict.
Clashes between rebels and government forces erupted for a second day in the Syrian capital on Monday, activists said, in some of the fiercest fighting to hit Damascus since the 17-month-old revolt against President Bashar al-Assad began.
"We have to live with the consequences of political failure, with the consequences of the brutality of this conflict on the lives and livelihoods of ordinary innocent people," Ging said.
Claus Sorensen, director-general of the European Community Humanitarian Office (ECHO), told reporters: "The real tragedy here ... is that with every hour and every day that passes without a political settlement, we will be faced with increased humanitarian needs."
Dorothy Shea, a senior official of the U.S. Bureau of Population, Refugees and Migration, called on all sides to allow unimpeded access for humanitarian agencies. The wounded and sick are being denied safe and equitable health care, she said.
"We note credible reports that individuals presenting themselves at hospitals and government-run health facilities have faced abuse from regime forces," Shea said in a statement issued later by the U.S. diplomatic mission in Geneva.
Ging said Syria's wheat harvest would fall by more than 700,000 tonnes this year, citing the result of a survey carried out by two U.N. agencies, the World Food Programme (WFP) and Food and Agriculture Organization (FAO), due to be issued soon.
"That is something we need to be prepared to cope with because there will be less wheat on the market," he told Reuters.
Syria consumes 4 million to 5 million tonnes of wheat a year but harvests over the last six years have fallen short of that, partly due to drought, forcing the country to import wheat.
The WFP - whose food rations are distributed by the Red Crescent - aims to feed 850,000 people in Syria in July, up from 500,000 in June, Ging said. "The principal challenge is insecurity on the ground and also a shortage in funding.
"The message from the humanitarian agencies is we need more money. If we don't get more money, people will die and there will be more humanitarian suffering," he said.
Two separate U.N. appeals - $180 million for humanitarian needs inside Syria and $193 million to help Syrian refugees who have fled abroad - are only 20 percent funded, he said.
Some 112,000 Syrian refugees have now registered with the U.N. refugee agency in four countries - Lebanon, Turkey, Jordan and Iraq, UNHCR official Panos Moumtzis told reporters. (Additional reporting by Khaled Oweis; Editing by Mark Heinrich)