In pictures: Ukraine on alert amid Russia intervention

Tensions have once again risen in Ukraine after defence sources in the country said Russia's military had given Ukrainian forces in Crimea a deadline to surrender - or else face attack.

A pro-Russian soldier blocks the Ukrainian naval base in the village of Novoozerne, Ukraine, on Monday, 3 March 2014 The threat came as Russian troops surrounded key Ukrainian installations. This pro-Russian soldier is seen blocking a Ukrainian naval base in the village of Novoozerne in western Crimea.
Pro-Russian demonstrators gather outside the headquarters of the Ukrainian Navy in Sevastopol on 3 March 2014. Russian naval officials have reportedly denied an ultimatum was given. Moscow has said its troops are needed in Crimea to protect civilians, many of whom are Russian speakers and have welcomed Russia's intervention. These demonstrators took to the streets of Sevastopol in a show of support for Russia.
A Ukrainian soldier speaks to his daughter through a gate as he waits inside the Sevastopol tactical military brigade base near Belbek in Sevastopol on 3 March 2014. The families of Ukrainian service personnel gathered around a base near Belbek as the country put its forces on full combat alert.
A woman looks through a damaged entrance door as pro-Russian demonstrators hold a rally outside the regional government building in Donetsk, 3 March 2014 Meanwhile, pro-Russian demonstrators occupied the regional government building in Donetsk, eastern Ukraine. Here, a woman looks through a damaged door as a rally continues outside.
A pro-Russian activist waves a chain after an unsuccessful attempt by the demonstrators to storm a regional state administration building in the Black Sea city of Odessa on 3 March 2014 This pro-Russian activist waved a chain in the air after protesters failed to storm a regional state administration building in the southern city of Odessa.
A woman cooks food for anti-Yanukovych protesters at Kiev's Independence Square, Ukraine, Monday, March 3, 2014. On Kiev's Independence Square, where protesters have been camped out for months, people denounced Russia's actions and said they would be willing to fight for Ukraine. This woman was cooking food for activists whose rallies led to the removal of former President Viktor Yanukovych in February.
Anti-war demonstrators hold signs as they take part in a protest against Russian intervention in Ukraine, on the sidelines of a EU Foreign Affairs Ministers meeting dedicated to the situation in Ukraine at the EU Council building in Brussels, on March 3, 2014 Demonstrators gathered outside the European Union Council building in Brussels as EU foreign ministers held an emergency session. The ministers condemned Russia's actions in Ukraine and demanded its troops return to their bases. Both the EU and US are threatening to hit Moscow with sanctions and travel bans.

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