MOSCOW - Secretary of State John Kerry arrived here today seeking a diplomatic solution to the protracted conflict in Syria. He'll meet with President Vladimir Putin and Foreign Minister Sergei Lavrov.

Russia is considered a lynchpin in the conflict. The Kremlin is a longtime ally of Syrian President Bashar al-Assad and has blocked previous attempts to sanction his government at the United Nations Security Council. Kerry wants to see if Russia's calculus has changed and whether it is willing to help convince Assad to step down. The Obama administration has long called for Assad to go, but Russia has rebuffed past efforts to change its mind, arguing that it is opposed to foreign intervention in the conflict.

"This is a time to talk to the Russians, to understand that from our side, we remain committed, and if they are as well, then we need to think about how to work operationally to make that happen," a senior State Department official told reporters on Monday, speaking on the condition of anonymity because of the diplomatic sensitivities.

"I don't know if we will get an agreement or not, but we certainly think it is worth testing and trying to find some ways forward," the official added.

Kerry's latest effort became all the more urgent in recent days as the Obama administration fends off calls for American military involvement after evidence has emerged that government forces may have used chemical weapons. Israel's airstrikes inside Syria over the past week also raised the stakes, heightening fears that the conflict could spread beyond Syria's borders.

Russia is reluctant to say so, but analysts say it has its own reasons to keep Assad in power. The Russian navy maintains a small, yet strategic base at the Syrian port of Tartus, which affords Russia a foothold in the Mediterranean. Syria has also been a large buyer of Russian arms and is Russia's last strategic ally in the Middle East.

Kerry's visit got off to an awkward start.

He had to hold at the airport for 30 minutes because his route into the city was blocked by columns of Russian tanks, ICBMs, and armored personnel carriers that are rehearsing for Thursday's Victory Day parade, when Russia celebrates its victory over Nazi Germany in World War Two.

He placed a wreath at the tomb of the unknown soldier near Red Square, then walked to the Kremlin for a meeting with President Putin. Before the trip, officials took pains to point out the significance of Secretary Kerry meeting with President Putin, who normally only meets with heads of state. Their meeting, however, was delayed by several hours for reasons that remain unclear.

After the Putin meeting, Kerry will sit down with Minister Lavrov and the two are expected to hold a press conference afterward.

Kerry's meetings are also expected to touch on the investigation into the Boston bombing suspects, who came from Russia's restive Caucasus region, as well as the diplomatic standoffs with Iran and North Korea.