Thick compressed ice and 'severe' conditions prevented the icebreakers and supply ships Sinegorsk and Johann Mahmastal from moving across the East Siberian Sea. Picture: Rosmorport

The icebreakers and the bulk carriers they were escorting became stuck some 24 nautical miles from Pevek, Russia's northernmost port, earlier in January.

Thick compressed ice and 'severe' conditions prevented the icebreakers and supply ships Sinegorsk and Johann Mahmastal from moving across the East Siberian Sea on their way to Arkhangelsk.

Their voyage had been a test of new climatic conditions, with Russia actively seeking to develop the Northern Sea Route between Europe and Asia, across the top of Siberia.

In the first such crossing since Soviet times, the convoy had earlier delivered supplies after a successful journey from Arkhangelsk to Pevek. Picture: Arctic Portal

In the first such crossing since Soviet times, the convoy had earlier delivered supplies for the world's first floating heat and power plant to be assembled in Chukotka, Russia's most easternmost region, after a successful journey from Arkhangelsk to Pevek lasting from 14 December to 7 January.

The ease of the sailing was seen as a sign that climate warming in the Arctic can open up shipping lanes even in midwinter.

But, despite significant temperature rises across the northern latitudes in recent years, the vessels became quickly stuck in thick, compressed ice on their return journey.

Initially there were hopes that the icebreakers could force their way out and continue their voyage within a week, and aerial reconnaissance was deployed in a search routes from the ice clog.

'The ice around Cape Shelagsky is at 10 points. The ice fields are more than one metre thick.' Pictures: Rosmorport, Alexander Samsonychev

But now a spokesman for Rosmorport has announced the icebreakers will delay a return until probably May or early June. 'The vessels will remain for the winter because of the very heavy severe ice conditions,' he said.

All the vessel got out of the ice, and three of them - Captain Dranitsyn and the two cargo ships - returned to Pevek. The Admiral Makarov moved further east to continue working for Rosmorport in clearing sea routes.

Officials said the icebreakers could have gone further through the ice but there was 'a very high risk of significant damage' to the supply ships, and it was decided to postpone the return to Archangelsk.

The icebreakers and the bulk carriers they were escorting became stuck some 24 nautical miles from Pevek, Russia's northernmost port. Pictures: Evgeny Basov, Chukotken.ru

Ruslan Nazarov, chief of Chukotka's emergencies service, said at the time the ships became stuck: 'The ice around Cape Shelagsky is at 10 points. The ice fields are more than one metre thick. The ice compression is strong and hummocks are higher than 2.5 metres.'

Emergencies Ministry officials denied the situation was an emergency. 'A winter stop is a good practice for preventing accidents related to complex ice situation,' said a source.

But the saga shows that despite all the talk of climate change and warming in the Arctic, thick ice can prevent convoys from crossing the Northern Sea Route in deep winter.