(Kevin Lamarque, Abraham Caro Marin/AP Photo)

After first rebuffing Russian invitations to meet, Secretary of State John Kerry is set to huddle with Russian Foreign Minister Sergey Lavrov on Friday in London, England, to talk about the turmoil in Ukraine.

The White House indicated today it was time for the two nations' top diplomats to sit down together again - even if, after weeks of talks, Russian President Vladimir Putin hasn't shown any signs of agreeing to U.S. and European demands that he pull back his military presence in the Ukrainian region of Crimea.

"We view it as appropriate for Secretary Kerry to meet again with Foreign Minister Lavrov to discuss again the situation, to make the case again for why a far better choice here would be to de-escalate and for Russia to pursue its interests through the means available to it that are legal and have the endorsement of the international community," White House press secretary Jay Carney told reporters today.

But why now?

Even as Kerry rejected over the weekend an invitation to visit Lavrov in Moscow, U.S. officials held out the possibility of a face-to-face meeting if Russia indicated it was willing to consider participating in a so-called "contact group" made up of European Union countries that would help mediate a resolution in Ukraine.

"The point is we're not going to just walk into something where they are just going to say, 'No, no, no, no, no,' to everything and we have traveled all the way there," a senior State Department official told reporters last week.

It's possible Russia has sent signals that Kerry would not leave empty-handed this week if he did meet Lavrov in person to discuss de-escalation in Ukraine.

Furthermore, Putin himself discussed the formation of a mediation group - as well as the presence of unarmed monitors in Crimea - during a phone call today with the chairperson of the Organization for Security and Cooperation in Europe (OSCE).

While not a groundbreaking move, Putin at least appeared willing to entertain the idea of a contact group, which last week he had rejected outright, with a spokesman saying such a proposal "make[s] us smile."

Another reason the United States may want to go forward with a face-to-face Lavrov meeting is that Crimea is holding a referendum vote Sunday on whether to officially become part of Russia - a move that Russia is encouraging. The United States and its allies have warned they'd consider this an illegal act, and have warned Russia to either back off or face increased sanctions.

"It can get ugly fast if the wrong choices are made," Kerry warned today, referring to the potential for added sanctions while testifying before the House Foreign Affairs Committee.

The fact that Kerry is meeting with Lavrov in person - and presumably wouldn't be getting on a plane without the assurance of at least some progress - is perhaps a final effort by the United States to avoid having to make things in Russia appear even uglier than they already are.