Britain, the United States, France and Ukraine blocked a Russian proposal at the United Nations to blacklist Syrian rebel groups Jaish al-Islam and Ahrar al-Sham for links to Islamic State and al Qaeda militants, diplomats said on Wednesday.
Russia made the proposal late last month and the U.S. mission to the United Nations had signaled it would oppose the move, saying it would undermine attempts to get a sustained halt in the fighting in Syria.
The U.N. Security Council's 15-member Islamic State and al Qaeda sanctions committee has to agree by consensus before individuals or groups can be blacklisted.
Jaish al-Islam (Islam Army) is a major armed rebel group in Syria and part of the High Negotiation Committee, which was set up in Riyadh last December to negotiate on behalf of opposition groups at U.N.-brokered peace talks with the government.
The High Negotiation Committee is backed by Western nations and key Arab states.
Ahrar al-Sham withdrew from the Riyadh meeting, saying "revolutionary groups" were sidelined. But the group did attend the last round of peace talks in Geneva.
Russia's Foreign Ministry has long said that Jaish al-Islam and Ahrar al-Sham should not be involved in Syria peace talks.
Ahrar al-Sham is an ultra-orthodox Salafist group and has fought as part of a military alliance including the al Qaeda-linked Nusra Front, which was not part of a cessation of hostilities agreement brokered in February.
Ahrar al-Sham, whose late leader fought alongside Osama bin Laden, last year denied sharing al Qaeda's ideology or having organizational ties to the group.