* More than 80 trucks set to cross Qamishli border
* Will be first U.N. aid shipment via Turkey
* Concern aid will only reach government-controlled areas
By Dasha Afanasieva
GAZIANTEP, Turkey, March 19 (Reuters) - A U.N. convoy of about 80 trucks is ready to cross the Turkish border into Syria for the first time, aid officials said on Wednesday, in a step they hope will pave the way for humanitarian access to the country's most desperate areas.
The convoy became possible after the U.N. Security Council last month unanimously called on Syrian authorities and rebels to allow prompt access for humanitarian supplies across front lines and borders by the most direct routes.
Last week, Syria granted its approval to the opening of the border crossing and sources said Turkey had also now given the delivery the go-ahead.
However, one Western official said the convoy would not reach some of the areas worst affected by the conflict, which has killed more than 140,000 people, driven 2.5 million to seek refuge abroad and displaced a total of 9 million.
"This is a significant step because it is the first U.N. convoy going across from Turkey into Syria since the conflict started," a senior aid official told Reuters.
The official added that non-governmental organisations had already been using Turkey's Nusaybin border post close to the Kurdish city of Qamishli inside Syria "for years" to convey smaller consignments of aid.
"Obviously we need more access," the official added.
Officials said the U.N. aid delivery was expected to take place soon but declined to give a precise timeframe.
"There will be U.N. organisations like UNHCR, UNICEF and maybe one or two others within that," a Turkish official said, referring to the U.N.'s refugee and children's agencies.
Syria's offer to allow aid into Qamishli has posed a dilemma for Turkey as it would open the border into an area of Syria largely controlled by fighters linked to the Kurdistan Workers Party (PKK) who have waged a three-decade insurgency in Turkey.
The offer also fails to provide direct access to rebel-held areas of northwest Syria most badly devastated by the civil war, which are further to the west in Aleppo and Idlib provinces.
The Western aid official said there were concerns that the aid would only reach the Kurdish areas of northeast Syria.
"If you go through that border crossing, you will not be able to reach the people that need this aid most - this is not a solution," he said.
He said Damascus had stipulated that the aid should be distributed by Syrian government partners, including the Syrian Arab Red Crescent, and that it was unlikely to cross front lines into the rebel-held areas.
"The U.N. will probably celebrate this as a great breakthrough. The question is what happens after," the Western official said.
Charities such as Save the Children have complained that the Feb. 22 U.N. Security Council resolution has not curbed Syria's suffering and say many sides in the conflict are failing to meet their obligations set out in the U.N. text. (Editing by Nick Tattersall and Gareth Jones)