DAVOS (Reuters) - U.S. Secretary of State John Kerry said on Thursday any delay to internationally brokered talks between Syria’s government and opposition groups would only be a matter of days, but there was still no sign of agreement on who will represent the opposition.

U.S. Secretary of State John Kerry smiles as he begins their meeting on Syria with Russian Foreign Minister Sergey Lavrov (not pictured), in Zurich, Switzerland, January 20, 2016. REUTERS/Jacquelyn Martin/Pool

Asked if he was concerned that a delay in the talks, due to start in four days in Geneva, may lead to a loss of momentum, he said: “When you say a delay, it may be a day or two for invitations, but there is not going to be a fundamental delay.

“The process will begin on the 25th and they will get together and see where we are,” he said at the start of a meeting with Israeli Prime Minister Benjamin Netanyahu in Davos.

The U.N. Special Envoy for Syria Staffan de Mistura said on Wednesday the talks may be delayed, but major powers must keep up the pressure to bring participants to the table.

Kerry met de Mistura in Davos on Thursday and held talks with Russian Foreign Minister Sergei Lavrov on Wednesday at which they both said talks should go ahead in January despite no sign of agreement on who should represent the opposition.

A Syrian opposition council backed by Saudi Arabia said on Wednesday it will not attend the negotiations in Geneva with the government if a third group takes part, a reference to a Russian bid to widen the opposition team.

Lavrov said there was no intention of delaying the talks into February and that he was confident the talks would take place in “in the next days, in January”.

Various dates were being mooted, but the final decision was for the U.N. Secretary General on the advice of de Mistura, he said.

De Mistura, who spoke in a CNN interview, was asked if he was able to send the invitations and replied: “I can’t tell you today, I will tell you on the 24th, one day before.”

He said it was important that it be “a serious talk about peace and not talks about talks”.

“I believe we can start the talks, perhaps not on the 25th, but we need to maintain the pressure, we need to maintain the momentum.”

De Mistura said he believed Russia, which has been carrying out air strikes against rebels in Syria for months, “has a great vested interest in not getting involved for too long”.

The United States was also “heavily involved politically” in seeking an end to the nearly five-year-old war, while Iran and Saudi Arabia had assured him they would work to end the Syrian conflict, despite their diplomatic row.

Russia and Iran, which support Assad, have rejected attempts by Saudi Arabia, which like the United States and European powers opposes Assad, to organize the Syrian opposition and delegation for the talks.

Iran’s foreign minister has said it was up to the U.N. to decide who represents the opposition, but he said 10 delegates at a recent opposition gathering in Saudi Arabia were members of al Qaeda - one of three groups he said must be barred.

On Thursday, Turkish Prime Minister Ahmet Davutoglu accused Russia of jeopardizing the talks by insisting on the inclusion of “terrorist groups” such as the Kurdish YPG militia on the opposition side.