Speaking at a humanitarian meeting hosted by Britain on the sidelines of

the G20 summit, Ban called on world powers to put aside their differences over the Syrian conflict, and to take concerted action to get desperately needed aid to the population.

"I must warn that ill-considered military action could cause serious and

tragic consequences, and with an increased threat of further sectarian

violence," Ban said.

About third of Syria's pre-war 20.8 million population has fled abroad or have been forced from their homes during the popular uprising against President Bashar al-Assad's regime which is now in its third year, UN refugee agency data showed.

"This is a humanitarian crisis of unprecedented proportions in recent

history," Ban said. But "as as some flee the country, others dig in to fight," Ban said, pointing to the need therefore to "avoid further militarisation of the conflict and revitalise the search for a political settlement instead."

With a political solution proving elusive as world leaders dig in their

heels over their entrenched positions, Ban called for unity in securing

humanitarian aid for the population.

A funding shortage was also threatening to leave refugees in neighbouring countries with no food, he said, adding that stocks would run out within days in Lebanon and within two weeks in Jordan.

"The world must do everything within its powers to stop the suffering of

the Syrian people. Let us use this united recognition of the problem as our starting point for focused and positive action," he said.

"Your support in exercising leverage on all parties to facilitate

humanitarian access is critical."