John Kerry, the US secretary of state, has said that the United States would double its non-lethal aid to opposition forces in Syria to $250m.

Kerry on Sunday stopped short of a US pledge to supply weapons to rebels fighting to overthrow Syrian President Bashar al-Assad.

He said, however, that the rebels' foreign backers were committed to continuing support and had decided to channel all future aid through the opposition Supreme Military Council.

Kerry added that "there would have to be further announcements about the kind of support that might be in the days ahead" if Syrian government forces failed to pursue a peaceful solution.

Speaking after a meeting of the Syrian opposition and its 11 main foreign supporters in Istanbul, Kerry said the United States would provide an additional $123m in non-lethal assistance to the rebels, bringing the total of this kind of US help to $250m.

Kerry urged other foreign backers to make similar pledges of assistance with the goal of reaching $1bn in total international support.

At a later news conference on Sunday afternoon, Kerry said he would push to ensure that new non-lethal military aid would be delivered as soon as possible.

'Breaking logjams'

Kerry said the equipment could include communications equipment, body armour, night vision goggles and medical supplies to assist the rebels.

Other supplies pledged by Kerry in late February, including ready-made meals and medical supplies, are only expected to be delivered by the end of this month.

Asked when the opposition could expect to receive the new supplies, Kerry told reporters:

"I can promise you that as soon as I return to Washington which is early this next week, I am going to press as hard I can to make sure that this is a matter of weeks that we are talking about ... this has to happen as quickly as possible."

Kerry said he had discussed ways to break the impasse during meetings with the Turkish Foreign Minister Ahmet Davutoglu, who hosted the meetings on Saturday between the Syrian opposition and their foreign backers.

"I am quite confident that some of those logjams are going to be broken," he said.

Kerry also said that an agreement by the foreign backers to channel future military assistance via the opposition's Supreme Military Council headed by Brigadier Selim Idris, would speed the delivery of supplies.

German stance

Germany took a clear stance that it would not be supplying any arms to Syrian rebels, but would give other forms of assistance.

"We Germans have decided that we will not deliver any weapons, but we will support the Syrian opposition in other ways," Guido Westerwelle, the German foreign minister, told German television channel ARD on Sunday, adding that Germany was the second biggest donor country.

Westerwelle said Germany considered directly delivering weapons to be problematic but added that Germany could not stop other countries from doing this.

"They can easily end up in the wrong hands and that is of course a danger for neighbouring countries and for the whole region and we want to prevent a conflagration," he said.

The US takes the same view.

Despite pressure from some members of Congress and recommendations even from among his own advisers, Barack Obama, the US president, has refused to supply arms to the rebels, reflecting concern that such weapons would fall into the hands of militants.