The trouble in Ukraine has left New Zealand in a critical position as it vies for selection to the United Nations Security Council, University of Otago politics professor Robert Patman says.

He said the heightened prospect of civil war in Ukraine, from Russia's incursion into Crimea, was ''the most challenging crisis for the world since the Syria situation''.

Foreign Minister Murray McCully had to move quickly to publicise New Zealand's stance on the issue, for favourable consideration in respect of Security Council selection in October, Prof Patman said.

Read more of the Herald's Ukraine coverage today:
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At the heart of Ukraine drama, a tale of two countries


''It's important that New Zealand, as a country running for Security Council, makes its position quite clear,'' he said.

The last time New Zealand had a seat on the council was 1993-94, and it hoped to get one for 2015-16.

Prof Patman said the tension over Ukraine could see New Zealand suspend its negotiations with Russia about a free-trade agreement.

New Zealand had strong economic ties to the European Union, which was likely to be among those imposing sanctions on Russia as a result of President Vladimir Putin's attempts for control in Ukraine, he said.

''New Zealand has quite substantial indirect economic interests in what's happening there, as well as big political interests.''

Prof Patman said there was unlikely to be all-out war over Ukraine, but the potentially crippling effect of sanctions should not be underestimated.

Gas was the main commodity exported from Russia to Western nations, and much of it went through Ukraine, he said.

''Putin is dependent on a strong economy, and no amount of land grabs will substitute that. If it [incursion into Ukraine] damages Russia's economy, he will pay a big price in the medium to long term.''

Prof Patman said there would be widespread anxiety among Ukrainian residents about Russia's dominance seeping outside Crimea.

Civil war was possible between western Ukranians, hoping for allegiance with the European Union, and eastern Ukranians with ties to Russia.

''Ukraine is divided over Russia. Some welcome what's happening, and the majority, I think, will be looking to the rest of the world to help them and prevent what may be an incursion by stealth.''

Mr McCully issued a statement yesterday, calling developments in Ukraine ''deeply worrying''.

He asked all parties to exercise restraint and refrain from any action which could escalate tensions.

''The sovereignty and territorial integrity of Ukraine must be respected and maintained.''

Mr McCully said the UN Security Council, which met yesterday to discuss the issue, was the appropriate body to ''take the lead''.

''We expect the council to live up to its responsibilities. It remains a matter of active consideration and the New Zealand Government is watching closely,'' he said.