Iran and the six major world powers will return to the table in Vienna on Tuesday for talks aimed at resolving their dispute over Tehran’s nuclear program.  But this uphill battle is likely to be made even more difficult by the Ukraine crisis.

The big question is, will Russia and China continue to support the west’s drive to end Iran’s nuclear program, which critics claim has the capability to make weapons but which Tehran says is only for power generation?  The two only reluctantly supported the past rounds of economic sanctions against Iran over its nuclear program between 2006 and 2010, and condemned US and European sanctions that targeted the country's lifeline oil exports.

But now, four of the parties at the Vienna talks are pushing through economic sanctions against Moscow that include asset freezes and travel bans on some senior Russian and Crimean officials.  China has more or less stayed out of it, but tends to back Russia in international issues.

So far, there hasn’t been any spillover from Russia’s occupation of the Crimean peninsula in Ukraine since the last round of talks two weeks ago.

“We hope that will continue to be the case,” said one western diplomat who spoke anonymously with the Reuters News Agency.  Another senior US official on Friday had said, “We all hope that the incredibly difficult situation in Ukraine will not create issues for this (Iran) negotiation.”

The six major world powers are the P5+1, made up of five “Permanent” (hence the “P”) members of the United Nations Security Council – The US, UK, France, Russia, and China, plus Germany.