In a hard-fought consensus decision, Russia has agreed to allow the OSCE to carry out a six-month monitoring mission in Ukraine.

The 57-member pan-European rights and security group will use the time to help diffuse the situation in the country, particularly in the violence-hit south-eastern areas.

A hundred civilian monitors will be deployed to Ukraine this weekend.

Daniel Baer, US Ambassador to the OSCE was keen to put the decision into action.

“We’re glad that the Russian Federation was able to finally come on board with a consensus resolution to send monitors to Ukraine,” he said. “As you heard from the Swiss chair, the decision itself calls for monitors to be deployed within 24 hours, which means that the first people will actually hit the ground either later tonight or tomorrow morning.”

But potential OSCE access to the controversial Crimea peninsula remains contentious.

The text of the OSCE decision mentioned reducing tensions “throughout the country” – referring to Ukraine. One Western diplomat reportedly described this as “constructive ambiguity” on the issue of Crimea.

On Friday, Russia signed a treaty to formally absorb Crimea from Ukraine and into the Russian Federation.

For Andrey Kelin, Russia’s Ambassador to the OSCE, the decision to allow a mission in Ukraine was straightforward.

“We proceed from the assumption that the mandate of mission is absolutely clear and it proceeds from the geo-political realities that have been (and) that are existing, since today,” he said. “Crimea has become a part of (the) Russian Federation.”

He went on to say the mission has “no mandate” to enter Crimea.

Earlier in March OSCE monitors had to abandon attempts to visit the Black Sea peninsula after warning shots were fired by unidentified armed men at the border.