ZURICH (AP) — U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov met on Wednesday in hopes of resolving differences over who is eligible to join U.N.-mediated peace talks for Syria due to begin next week. Those differences have threatened to delay the start of the negotiations.

The State Department said the two men had discussed plans for the negotiations that the U.N. special envoy for Syria, Staffan de Mistura, hopes to convene in Geneva on Jan. 25 and "the importance of maintaining progress toward a diplomatic solution to the crisis." But, while both sides said they did not support a delay in the talks, it was not immediately clear if the differences had been resolved.

"We do not have any kind of thoughts about changing the beginning of the talks from January to February," Lavrov told reporters. "This is the position of Russia and the USA."

"The political process will begin, we hope, in the nearest future, during January," he said. "Various dates have been named, but the final decision will be taken by the Secretary-General of the United Nations on the advice and recommendations of his special envoy Staffan de Mistura."

Lavrov added that the main topic of conversation with Kerry was "coordination," primarily about terrorist organization, which would be left out of the political process as well as a ceasefire that is envisioned to take effect once the negotiations begin.

In the meeting, Kerry also called for Russia to use its influence with Syrian President Bashar Assad "to ensure immediate, unimpeded and sustained humanitarian access to all Syrians in need," State Department spokesman John Kirby said, particularly in besieged communities like Madaya, where deaths from starvation have been reported.

The negotiations between the Assad government and the opposition are to be the first step in a proposed 18-month political transition for Syria, which has been mired in civil war for four years.

Differences over which Syrian opposition groups should be labeled terrorists and barred from the negotiations and the ceasefire have led to concerns that the talks may have to be postponed.

Russia and Iran, which back Assad, have immense differences with Saudi Arabia, other Arab states, the United States and Europe over which opposition groups should be considered terrorists and therefore excluded from an 18-month political transition process the U.N. has endorsed.

One dispute is over the groups Ahrar-as-Sham and Jaish al-Islam. Russia and Syria consider terrorists; Saudi Arabia, the United States and others view as legitimate opposition groups.

On Monday, U.N. chief Ban Ki-moon urged countries backing opposing sides in the Syrian conflict to redouble efforts to reach agreement on the eligible opposition groups. But, U.N. officials say they can't send out invitations until the key countries agree on an opposition list.

Kerry will be visiting Saudi Arabia this weekend in order to pursue a consensus on the list.

In Zurich, Kerry and Lavrov also discussed the situation in Ukraine and compared notes on how to speed up the full implementation of an agreement to end hostilities in the east, where government troops are continuing to battle Russia-backed separatists, Kirby said. The two also discussed possible responses to North Korea's latest nuclear test, he said.

Kerry left the meeting in Zurich to participate in the World Economic Forum in the Swiss resort town of Davos, where he will see a number of world leaders over the next two days, including Israeli Prime Minister Benjamin Netanyahu and Iraq's prime minister.

Associated Press writer Jim Heintz in Moscow contributed to this report.