* U.N., EU urge Syria to lift aid obstacles
* EU pledges 147 million euros in aid
* WFP chief says situation continues to worsen
By Adrian Croft
BRUSSELS, Dec 18 (Reuters) - The heads of the U.N. and European Union aid agencies called on Wednesday for a "humanitarian ceasefire" in Syria to allow convoys to deliver help to areas that aid workers cannot reach.
The officials urged all sides in the Syrian war to allow free access for humanitarian groups, saying aid should not be held hostage to political or military considerations.
Calling the Syria conflict the "greatest humanitarian tragedy of our times", the aid chiefs said they feared the worst as another harsh winter threatened even greater suffering.
The statement was issued by U.N. emergency relief coordinator Valerie Amos, U.N. High Commissioner for Refugees Antonio Guterres and the heads of the U.N. Children's Fund, Anthony Lake, and World Food Programme (WFP), Ertharin Cousin, with EU humanitarian aid chief Kristalina Georgieva.
The U.N. leaders were in Brussels to sign contracts which committed the European Commission to provide 147 million euros ($202 million) in aid to people affected by the Syrian crisis.
Aid workers have regularly complained that restrictions have been placed on their movement in Syria, particularly by the government of Syrian President Bashar al-Assad.
Blockades have been used mostly by the government but also on a smaller scale by rebels to prevent food and medicine entering besieged areas.
"A humanitarian ceasefire would allow aid convoys to deliver assistance to communities which remain out of our reach," the statement by the U.N. and EU leaders said, without specifying whether they wanted a national or a local ceasefire.
Some 9.3 million Syrians needed help, the number of internally displaced had grown to 6.5 million and more than 2.2 million refugees had fled the country, the statement said.
The United Nations appealed this week for a record $6.5 billion for Syria and its neighbours to help 16 million people, many of them hungry or homeless victims of a conflict that has lasted 33 months.
The European Commission and the EU's 28 member states have donated more than two billion euros since the start of the Syria crisis, making it the biggest donor, the EU said.
WFP Executive Director Cousin said the humanitarian situation in Syria continued to worsen.
Access problems limited the organisation's ability to reach people in need in many areas of Syria, including in both government and opposition-held zones, she told Reuters in an interview.
"The primary challenge is the areas where there is ongoing conflict ... There is blame that you can place on both sides of this conflict," she said.
"We work to be as innovative as possible, to find roads that one day may be inaccessible because they are besieged ... but the next day we can access it, so we are doing everything possible to reach as many people as possible," she said. ($1 = 0.7283 euros) (Editing by Sonya Hepinstall)
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