On the ground, one of the major flashpoints in the Ukrainian war is the Zaporizhzhia nuclear power plant. The facility is Europe's largest, and was seized by Russian troops in March. It saw shelling last week, with Kyiv and Moscow blaming each other for the attack. Foreign ministers from the G7 group of industrial powers have urged Russia to "immediately hand back control" to Ukraine, warning that a failure to do so raises the risk of a nuclear accident. Russia is very unlikely to do so. What exactly happened when a series of explosions hit a Russian airbase in Crimea is still becoming clear. Ukraine has said several Russian warplanes were destroyed; Russia denies this and that the explosions were the result of an attack. Crimea was annexed in a disputed referendum by Russia in 2014. Internationally it is still seen as part of Ukraine. An attack by Ukraine on Russia in Crimea would be a major escalation. But Ukraine has denied responsibility for the blasts, which Russia says were caused by ammunition being detonated. In one of his regular addresses Ukrainian President Volodymyr Zelensky said: "This Russian war...began with Crimea and must end with Crimea - with its liberation."

Is Russia struggling to find troops for Ukraine? 

By Vitaliy Shevchenko, BBC Monitoring

There are indications the Kremlin is running out of troops for its war with Ukraine. Regional authorities in Russia are pursuing a campaign to recruit volunteer fighters, but it is not getting much traction, one report says.According to independent Russian website Mediazona, at least 25 Russian regions are now trying to form volunteer battalions. "The local authorities are sparing no effort in advertising the battalions or reporting about them in the media, but the results of their efforts fail to impress," Mediazona says. Local administrations are offering lavish payments for fighting in Ukraine, but some have found only a fraction of the fighting force they are trying to assemble, the report says. Earlier today, the UK Ministry of Defence said the volunteer battalions being raised across Russia will likely form a large part of a new army corps. However, "given very limited levels of popular enthusiasm for volunteering for combat in Ukraine", it will probably be difficult for Russia to find the required number of troops, the British military said. Several independent Russian media outlets said last week the private military company known as Wagner was trying to recruit fighters for Ukraine among inmates at Russian jails.