PARIS — The top U.S. and Russian diplomats met Monday to try to accelerate frustratingly slow peace efforts in Syria, where the signs point only to a worsening conflict.

Capping off an eight-day trip to the Middle East and Africa, Secretary of State John Kerry flew into the French capital to see Russian Foreign Minister Sergey Lavrov and exchange updates on their respective diplomatic efforts.

The United States and its Arab allies are attempting to secure the participation of Syria’s fractured opposition at an international peace conference in Geneva, planned for next month. Russia is pledging to deliver Syrian President Bashar Assad’s regime to the talks.

But despite claims of progress by both, there is little evidence to suggest either side is ready to halt more than two years of violence that has killed more than 70,000 people. President Barack Obama has demanded that Assad leave power; Russia has stood by its closest ally in the Arab world.

The one-on-one Paris meeting between Kerry and Lavrov, to be immediately followed by a dinner that includes French Foreign Minister Laurent Fabius, comes as Sen. John McCain slipped into Syria Monday to meet with rebels and at an increasingly dangerous time for the country.

For the past week, regime troops and allies from Lebanon’s Hezbollah — and even some Iranian fighters — have waged an offensive in Qusair, gaining ground against the rebels behind intense bombardments of the strategic western Syria town.

Hezbollah’s enhanced role poses an assortment of concerns for the Obama administration, with the group’s leader, Hassan Nasrallah, vowing over the weekend that his militants would back Assad to victory.

Beyond providing powerful reinforcements to Assad’s regime, Hezbollah’s involvement increases the risk of spillover into Lebanon, a country as ethnically divided and fragile as Syria. Two rockets struck a Hezbollah stronghold in southern Beirut on Sunday, raising fears that the country could be plunged back into civil war.

And any conflict with Hezbollah threatens to drag in Israel, which has proved with airstrikes it won’t tolerate large-scale and advanced weapons transfers to its northern border. Lebanon’s state-run news agency reported one missile fired from that area toward the Jewish state on Sunday night.

For Kerry and other would-be peacemakers, the confluence of developments only reaffirms the need for a serious peace process to begin.

The Americans have stressed that any talks be carried out in good faith and lead to the full transfer of power to an interim government. Logic, they say, compels that this government not include Assad or other members of his government culpable in widespread abuses.