The unscheduled meeting, taking place on the side of a wider international security conference in Dublin, Ireland, marks an intensification of diplomacy just three days after CBS News reported Syria's isolated regime was preparing its chemical weapons for use in bombs.
U.S. officials tell CBS News the meeting may be a sign that Russia is now willing to consider supporting further U.N. action against Syrian President Bashar Assad's regime -- to send a message that he must stop his deadly assault on rebels forces and areas they control. Opposition officials say the 21-month assault has left more than 40,000 people dead.
Russia, one of Assad's few remaining allies, has thus far opposed any U.N. measures against him, and the U.S. and Russia have remained at odds over the level of the threat posed by Syria's weapons stockpiles.
If Clinton can cement Russian support and reach a compromise in her meeting with Lavrov on Thursday, the U.N. Security Council might be able to pass a resolution implementing harsh economic sanctions against the Syrian regime, -- possibly cutting it off from all of its remaining financial support. Both Russia and China have used their veto power as permanent members of the Security Council to block any such resolutions thus far. It remains unclear how China would react if Russia were to get behind tougher sanctions.
The key sticking point in a peace plan forged by Brahimi's predecessor, Kofi Annan, which was agreed to by both Russia and the U.S., was a provision aimed at forcing the Syrian regime to comply with terms of a phased cease-fire. Russia vetoed a Security Council resolution that would have put the threat of international punitive measures against Syria in place for failure to comply.
If Brahimi is hopeful of striking a similar deal now, or reviving the one crafted by Annan, getting the U.S. and Russia on the same page on how any cease-fire terms are enforced on Assad's regime -- or even whether they are enforceable -- will be crucial.
On the ground, rebels have now surrounded the Syrian capital of Damascus, threatening Assad's stronghold. In recent days, Clinton has said that an increasingly threatened Assad regime may resort to extreme measures -- even using its stores of chemical weapons -- to try to maintain its grip on power.
CBS News correspondent David Martin reported Monday that Assad's regime had begun preparing its chemical weapons for use. Martin said orders had been issued in Syria to bring together chemical ingredients that are normally stored separately for safety, but that form the deadly nerve agent sarin when they are combined.
The Syrian government, meanwhile, refuses to even confirm that it possesses chemical or biological weapons.
"I assure you that Syria does not own banned weapons, and if we just admitted -- hypothetically speaking -- if Syria had all the weapons in the world, it would never use it against anybody, neither inside Syria, nor abroad," Syrian Information Minister Omran Ahed al-Zouabi told CBS News correspondent Elizabeth Palmer in a November interview. "The real reason for this, is that we believe that acquiring chemical, biological and nuclear weapons, as in the case with Israel, is gravely immoral."
The U.S. government said Wednesday, meanwhile, that it was aware of several offers of asylum made to Assad and his family by countries in the Middle East and elsewhere, if he were to agree to leave his position. Clinton told CBS News in September that the Russians had refused to offer Assad asylum. It is unclear whether he'd be able to negotiate an exit, however, as the U.S. the U.N. and the Syrian opposition have said he should not be permitted to evade justice.
Next week, Clinton will attend a meeting of the "Friends of Syria" in Marrakesh, Morocco, and it is expected that the U.S. will officially recognize a newly-formed Syrian opposition group as the sole legitimate representative of the Syrian people, helping to pave the way for a new government to take shape even with Assad still in power. Several European and Middle Eastern nations have already recognized the coalition as the sole representative.2012 CBS Interactive Inc. All Rights Reserved.