Spark that could ignite this tinderbox: IAN BIRRELL on how Ukraine's 'anti-terrorist' operation could lead to a full-scale invasion from Russia

This is the long-dreaded moment. It is seven weeks since a strange struggle in the east of Europe began, with the silent invasion of Crimea by Russian special forces stripped of their insignia and supported by well-armed local militia to quash any dissent.

Despite the seizure of the peninsula – the first major land grab in Europe since 1945 – both sides sought to avoid conflict knowing the regional tinderbox could explode.

Moscow wanted the annexation of Crimea to pass peacefully to demonstrate that its citizens supported the takeover. Ukraine, a weak and bankrupt state run by an interim government following the ousting of a pro-Russian president, aimed to avoid a conflagration that could rip it apart and destroy any hopes of democracy.

Making moves: Ukraine's federalisation supporters, members of the People's Militia of Donbass seize a police station in Kramatorsk

Attack: rmed pro-Russian activists stand outside the police station in the eastern Ukraine town of Kramatorsk But now everything has changed. In recent days, pro-Moscow forces have seized police stations and security buildings, barricading themselves in, flying Russian flags and demanding breakaway referendums just as in Crimea. They threw down a gauntlet, and authorities in Kiev had no option but to respond. RELATED ARTICLES Previous

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Next Ukrainian president says it is 'war' between his country and... Kiev government to deploy troops in Ukraine's east

Anti-Kremlin protest draws thousands in Moscow Share this article Share Previous demonstrations in the Russian-speaking east of Ukraine appeared largely to involve local people. But events over the weekend were different, with the arrival on buses of well-organised, well-trained and well-armed forces, wearing identical uniforms to those I saw in Crimea last month. At least half a dozen cities were targeted. No country could allow such incidents of insurgency on its territory. But Ukraine’s efforts to dislodge these gangs – which led to casualties on both sides yesterday – risk sparking a full-scale intervention by the Kremlin to ‘defend’ the region’s Russian speakers. It is a threat that terrifies Ukraine’s new political masters – and, indeed, the rest of the continent – after Nato released aerial photographs last week revealing the extent of Russian military build-up on Ukraine’s borders.

Armed pro-Russian activists pose for a photo after they occupied the police station in the eastern Ukraine town of Slovyansk

Pro-Russia supporters beat a pro-Western activist who lies on the stairs during a pro Russian rally in Kharkiv, Ukraine, Sunday

What is Putin’s gameplan? His invasion of Crimea was probably a pragmatic response to the ousting of his ally, fuelled by fear of Ukraine slipping out of Russian control and into the arms of Europe. Now he has seen his popularity soar on a surge of nationalist fervour, with even Mikhail Gorbachev’s former aides talking about the ‘inevitable’ restoration of ‘a state like the Soviet Union’. This could make it difficult to back down, even if he wanted to do so.

None of the eastern Ukrainian regions want unification with Moscow, according to polling. But analysts believe Putin wants to keep the state as weak and unstable as possible.