And in another sign of Russian concern about the situation on the ground eight months into its invasion, the Kremlin-installed chief of the strategic southern region of Kherson on Tuesday announced an "organised, gradual displacement" of civilians from four towns on the Dnipro River.Russian forces in Kherson have been driven back by 20-30 km (13-20 miles) in the last few weeks and are at risk of being pinned against the western bank of the 2,200-kilometre-long (1,367-mile-long) Dnipro river that bisects Ukraine.Register now for FREE unlimited access to Reuters.com"The situation in the area of the 'Special Military Operation' can be described as tense," Sergei Surovikin, a Russian air force general named this month to take charge, told the state-owned Rossiya 24 television news channel.After staging referendums in September that Ukraine and its allies said were illegal and coercive, Putin proclaimed the annexations of the eastern border provinces of Donetsk and Luhansk - together forming an important industrial region known as the Donbas - as well as Kherson and Zaporizhzhia in the south.Ukraine has invited United Nations experts to inspect what it says are downed Iranian-origin drones used by Russia to attack Ukrainian targets, in violation of a U.N. Security Council resolution that endorsed the 2015 Iran nuclear deal, according to a letter seen by Reuters."