U.S. Secretary of State John Kerry (R), Russia's Foreign Minister Sergei Lavrov (L) and U.N-Arab League envoy for Syria Lakhdar Brahimi talk after their joint news conference at the U.S. Ambassador's residence in Paris January 13, 2014. REUTERS/Pablo Martinez Monsivais/Pool

MOSCOW (Reuters) - Russia’s foreign ministry said on Monday that U.S. Secretary of State John Kerry and his Russian counterpart Sergei Lavrov had agreed in a phone call on the preconditions necessary for another meeting of world powers on Syria.

Kerry had previously said the aim was to hold a third round of talks in New York on Dec. 18. It was unclear whether the agreement on preconditions -- which came ahead of a planned visit by Kerry to Moscow on Tuesday -- meant the Dec. 18 meeting was on or off.

The Russian foreign ministry said in a statement that the two men had agreed that the make-up of an opposition delegation that could conduct talks with the Syrian government had to be prepared before another meeting along with an agreed list of Islamist terrorist groups to be jointly fought against.

It said Kerry and Lavrov had also confirmed the importance of respecting the principle of consensus at the meeting when it happened and of ensuring that all of the group’s members took part in the talks.

Russia, the United States, European and Middle Eastern countries agreed in Vienna last month on a two-year timeline leading to Syrian elections, but left many questions unresolved, most notably the fate of Syrian President Bashar al-Assad.