Oren Dorell

USA TODAY

As Ukraine's standoff with Russia over its support of pro-Russian separatists escalates, President Obama must decide how the USA can prevent the conflict from spinning out of control.

While Obama has been quietly letting Germany take the lead on the diplomatic front up until now, what he and his deputies communicate at talks Tuesday between Ukraine, Russia and European leaders in Belarus could play a pivotal role in whether Russia succeeds in disabling Ukraine's economic recovery and permanently destabilizing Europe's second-largest country.

Phillip Karber, who has briefed the White House and Congress on the Ukrainian military's needs in its fight against separatists, says the USA should provide Ukraine with Predator drones to help stem the flow of armored reinforcements that have crossed from Russia.

"For every battalion of combat material or troops the Russians send into Ukraine, the U.S. should send a team with a MQ-9 Predator," said Karber, who is president of the Potomac Foundation, a think tank. "(The Predator) is not only very effective against dispersed armored vehicles, but greatly reduces collateral damage that comes from ground-attack aircraft."

On Friday, NATO Secretary General Anders Fogh Rasmussen said Moscow has sent Russian-manned artillery units into Ukraine in recent days and was using them to shell Ukrainian forces as part of a "major escalation" of Russian involvement in the disputed region.

Russia continues to deny that it is supplying weapons and other military aid to the separatists in Ukraine, with the Russian foreign ministry calling Rasmussen's statement "another lie" on Saturday, Russian news agency RIA Novosti reported.

Other analysts warn dramatically increasing military aid to Ukraine risks a rapid Russian escalation that the USA could not match.

Russian President Vladimir Putin — who has at least 10,000 troops on Ukraine's border, according to NATO — "can escalate more with less cost" than the USA can, says Bruce Jones, director of the Project on International Order and Strategy at the Brookings Institution in Washington. That "could create a much more intensive war with high costs for Ukraine."

Instead, Obama has taken a measured approach that includes providing Ukraine with U.S. intelligence support, military training and advice while gradually imposing sanctions that hurt the Russian economy without causing it to collapse, Jones said.

However, Jones says the president hasn't done a good job of explaining that approach to the American public and the international community.

"Obama hasn't made it clear he's willing to escalate if Putin does," Jones said. "That lack of certainty Putin can exploit. If he's not certain we will escalate, for him the risk of escalating is less."

The USA needs to make clear that it will do whatever it takes to help Ukraine regain control of its territory in the east, says Janusz Bugajski, a senior fellow at the Center for European Policy Analysis, a Washington think tank.

"We don't want another divided state in Europe in which Russia can pull the strings and keep it unstable," Bugajski said. "If it's come to the point the Ukrainians can't take back their territory … then I think it's time to help the Ukrainians regain the initiative."

That should also guide whether the USA continues to let Germany take the lead in negotiations after Tuesday's talks, Bugajski said.

"The bad outcome is if the Germans and Europeans with Russia somehow push Kiev to accept a peace deal or cease-fire that acknowledges the existence of this rebel enclave, then it's time for the United States to step in because that would be the worst-case scenario."

German Chancellor Angela Merkel called for a cease-fire during her visit Saturday to Kiev, where she met with Ukrainian President Petro Poroshenko.

"The significance of my visit is that the German government (believes) that the territorial integrity and well-being of Ukraine is essential," Merkel said, according to German newspaper Deutsche Welle.

Poroshenko pledged that Ukraine "will do everything for this to happen but not at the expense of the sovereignty, territorial integrity and independence of Ukraine."

Tuesday's talks follow the entrance and exit of a Russian aid convoy into Ukraine, a move that drew international condemnation and a threat by the White House to increase sanctions if the trucks did not leave immediately.

The Kiev government called the vehicles' crossing into Ukrainian territory a "direct invasion." Russia said the trucks carried food, water, generators and sleeping bags to Luhansk, a pro-Russian separatist stronghold in eastern Ukraine.