* "Watching tragedy unfold," U.N. aid chief says
* Rebels say 3 million in their areas need help
* Amos says Syria still refusing aid via Turkey
* U.S. calls for "direct, cross-border delivery"
By Stephanie Nebehay
GENEVA, Feb 19 (Reuters) - The rebel-held north of Syria remains largely out of reach to aid operations, even though they have been stepped up elsewhere in the country torn by civil war, U.N. humanitarian chief Valerie Amos said on Tuesday.
"We are watching a humanitarian tragedy unfold before our eyes," Amos told a news briefing. "We must do all we can to reassure the people that we care and that we will not let them down."
Syrian opposition representatives told the United Nations this week that some three million people living throughout rebel-held territory require international assistance, she said.
The Syrian government still refuses to allow U.N. convoys to cross from Turkey into northern Syria, as most border crossings are controlled by the Free Syrian Army, she said.
Four million Syrians were deemed in need of aid late last year, but the situation has deteriorated since due to shelling, inflation, and shortages of food and medicine, she said.
Some 70,000 people have been killed in the nearly two-year-old revolt against President Bashar al-Assad that has also sent 860,000 refugees fleeing abroad, according to the world body.
Typhoid has broken out in an rebel-held Deir al-Zor due to people drinking contaminated water from the Euphrates River, the World Health Organization (WHO) said on Tuesday.
In the last few weeks, the U.N. refugee agency reached rebel-held Azaz with aid for the first time. WHO has delivered vaccines in many opposition-held areas, Amos said.
"Cross-line operations are difficult but they are do-able.
"We are crossing conflict lines, negotiating with armed groups on the ground to reach more in need. But we are not reaching enough of those who require our help. Limited access in the north is a problem that can only solved using alternative methods of aid delivery," Amos said.
She held talks with Suhair al-Atassi, a vice president of the opposition Syrian National Council, on Monday. Syrian deputy foreign minister Hossam Eddin attended the closed-door Geneva forum on Tuesday but opposed the rebels taking part, she said.
The Syrian government has agreed that 3 more international agencies could deploy aid workers - Mercy Corps, NRC and Merlyn - bringing the total to 11, but still not enough, Amos said.
"With respect to the Turkish border, I have spoken to the (Syrian) government on a number of occasions about allowing us to bring in supplies across that border. My last conversation with them was yesterday. The answer remains no," Amos said.
The U.N. must uphold General Assembly resolutions requiring consent of a government to allow relief goods to be imported, unless authorised by a Security Council resolution, she said.
It is importing fuel, vital for convoys and U.N. aid operations, via Lebanon with Syria's permission, she said.
LIMITED AND DIFFICULT ACCESS
John Ging, director of operations for the U.N. Office for the Coordination of Humanitarian Affairs, said that most goods are imported via Lebanon and Jordan, with Syria's permission.
"They are opposed to operations across borders that they don't control," Ging told Reuters in an interview on Tuesday.
"The reason it's significant and important for us is that our access across the conflict line from within to those areas (on the Turkish border) is very limited and very difficult and dangerous. As a result, we're not getting adequate or anything even close to an adequate humanitarian supply into those areas."
Claus Sorensen, director-general of the European Union Office for Humanitarian Aid who attended the Geneva forum, said it would be far better and safer to bring in aid through Turkey.
"This is very much what was the discussion was about today," Sorensen told reporters.
The United States, which announced a further $19 million aid contribution, called for "direct, cross-border delivery". (Reporting by Stephanie Nebehay; Editing by Michael Roddy)
See ways below to help those fleeing to refugee camps in neighboring countries:
UNICEF is collecting funds dedicated to the immediate needs of displaced Syrian children. As winter sets in, the organization is focused on addressing the challenges a colder climate brings to some of the conflicts most vulnerable victims. Learn more here.
The UN refugee agency is leading the Syrian refugee response. The organization has camps in Jordan and continues to offer humanitarian assistance in neighboring Lebanon and Iraq. With thousands fleeing Syria every day, the organization is working to keep up. Learn more here.
Mercy Corps has been working in Syria since 2008. Now with the escalating humanitarian crisis, the organization is responding to the needs of refugees in Lebanon and Jordan refugee camps -- increasing access to clean water and providing psychological support for children. Learn more here.
International Red Cross
The ICRC and the Syrian Arab Red Crescent are working together to feed the millions of Syrian refugees, provide medical care to those in need and war-surgery training to doctors treating casualties in neighboring Lebanon. Learn more here.
Save The Children
In response to the humanitarian crisis and plummeting temperature, Save The Children is providing children with warm blankets, shoes, clothes and winter-aid packages for infants. Learn more here.
War Child, a UK-based charity dedicated to helping children affected by conflict, has been working in Lebanon creating six ‘safe spaces’ in schools to provide art and music therapy for affected children and has helped 400 youngsters enroll in school. Learn more here.