Russian foreign minister warns west over ?aggressive line? in Ukraine crisis

Russia's top diplomat has warned the west that its "aggressive" approach to Ukraine and threat of sanctions could force Moscow to "eliminate unacceptable threats to our security", after a high-stakes conversation between Vladimir Putin and Joe Biden failed to deescalate the crisis.

The remarks by the Russian foreign minister, Sergei Lavrov, were published shortly after the Russian and US presidents held a 50-minute telephone call in which the two sides traded threats regarding tensions over Ukraine.

During the phone call, Biden told Putin that the US would impose serious sanctions on Moscow in the event that Russian forces, which include tanks, artillery and even short-range ballistic missiles, launched an attack on Ukrainian forces.

Yuri Ushakov, a Kremlin aide, said Putin responded that fresh sanctions could lead to a "complete breakdown in ties between our countries". "Our president also mentioned that it would be a mistake that our descendants would see as a huge error," Ushakov told reporters late on Thursday evening.

The US and other western countries have said Russia is massing military equipment on Ukraine's border for what could be a potential invasion force. Thousands of Ukrainian civilians have taken part in combat training in preparation for a potential Russian assault, although the situation in the country is largely normal ahead of the new year holiday.

Earlier this week, the secretary of Ukraine's national security council, Oleksiy Danilov, said Kyiv was concerned about Russian troops on the border but added that there was no panic. He said: "As for the troop buildup near our borders reported by foreign media - we do not see that. There is a certain increase of [Russian] military and we closely monitor what's happening at our borders."

Ukrainian military intelligence had previously warned of a massive buildup of Russian military equipment on the border and the potential of a large-scale Russian offensive by mid-January. Russian delegations are set to meet then with US, Nato, and Organisation for Security and Cooperation in Europe (OSCE) officials for a series of high-stakes talks on European security.

Lavrov, in an interview with the news agency RIA Novosti, said Russia insisted on US and Nato military officials taking part in the negotiations next month. Moscow would not allow the talks to be dragged out by western nations, he said.

"If there is no constructive response within a reasonable time and the west continues its aggressive line, then Russia will be forced to take all necessary measures to ensure strategic balance and eliminate unacceptable threats to our security," Lavrov added.

An analysis by the Conflict Intelligence Team, a group of bloggers and analysts who collect open-source intelligence on Russian military movements, showed that Russian military equipment had continued to arrive in the area to the north-east of Ukraine and to Crimea in the past month.

The group concluded that "by the new year the concentration of vehicles near Ukraine's borders and in Crimea has reached an unprecedented scale, most likely surpassing the April figures". Russia held a massive buildup of troops earlier this year, leading to a summit between Putin and Biden in Geneva in June.

However, Moscow is not yet ready to launch the operation, the group noted, adding that a limited strike on the Ukrainian military was more likely than a large-scale operation to seize and hold territory.