LONDON : Russia is again building up forces on the border with Ukraine, NATO Secretary-General Anders Fogh Rasmussen said on Thursday, calling it a “very regrettable step backwards”.

Rasmussen said “at least a few thousand more” Russian troops had been deployed to the border. “I consider this a very regrettable step backwards. It seems that Russia keeps the option open to intervene further into Ukraine,” he told an audience at the Chatham House foreign affairs think-tank in London.

Rasmussen said he expected the West to meet any further Russian incursions into Ukraine in a “firm manner” with more stringent economic sanctions. He said if the Russian deployment was intended to seal the border and stop the flow of equipment and weapons into Ukraine, it would be a “positive step”.

But he added: “I also have to say that is not exactly what we are seeing.”

Ukraine’s new president Petro Poroshenko is currently pushing for a ceasefire in the separatist east following 10 weeks of unrest. But fighting which has now claimed around 360 lives has continued unabated.

Poroshenko has also appealed for US and EU help to secure the porous border with Russia and stem the influx of arms and militants.

Rasmussen said Russia’s actions in Ukraine were a “wake-up call” for the international community at a time when defence budgets were being cut in many countries, including Britain.

He said that while there had been a 50-percent increase in Russian defence spending since 2008, NATO nations’ spending on the military had dropped by around 20 percent.

“Russia’s aggression against the Ukraine is an attempt to rewrite international rules and recreate a sphere of influence,” Rasmussen said.

“The illegal Russian military actions in Ukraine are a wake-up call - a reminder we cannot take security, we cannot take freedom, for granted. We have to invest sufficiently in security and defence.”