Matthew 
Russian forces are making gains in the Ukrainian north-eastern region of Sumy – a development that may be linked to Moscow's attempts to create "buffer zones" along the border, Ukrainian regional authorities have said.
The head of the Sumy region Oleh Hryhorov said Russian forces have seized four villages and that fighting is continuing near other settlements in the area "with the aim of setting up a so-called 'buffer zone'".
Russia maintains it has captured six villages in Sumy so far.
Last week, Russian President Vladimir Putin announced a plan to create "security buffer zones" along the border. "Enemy firing points are being actively suppressed, the work is under way," he said.
The buffer zones would be created to provide "additional support" to areas in Russia which border Ukraine's Kharkiv, Sumy and Chernihiv regions, Putin said.
In a statement on Facebook on Monday, Sumy's Hryhorov wrote: "The enemy is continuing attempts to advance with the aim of setting up a so-called 'buffer zone',"
He added that the villages of Novenke, Basivka, Veselivka and Zhuravka – all in Sumy – had been occupied.
Kyiv has not yet officially stated that Russian troops are in the Sumy region and, when contacted by the BBC, Hryhorov declined to confirm the information he shared on Monday, saying only the military could comment on front-line activities.
The General Staff's daily briefings only mentioned clashes and other military activities in "the Kursk direction" – meaning towards the border with Russia – without naming any specific locations.
The Ukrainian army's group of forces that coordinate military activities in the region declined the BBC's request for comment, indicating that information about the Russian advancement in the north is an extremely sensitive issue for Ukrainian authorities.
However, in his address on Monday night Ukraine's President Volodymyr Zelensky mentioned Russia's "preparation for new offensives" – which was largely interpreted as a reference to the events in the Sumy region.
Deep State map, a group that monitors the latest front-line developments in Ukraine, marked four Ukrainian villages as fully controlled by Russian forces even before Hyrhorov's announcement.
Deep State's co-founder Roman Pohorily said that Russian troops have been pushing in those areas since March.
Ukrainian military observer Kostyantyn Mashovets confirmed this, although he pointed out that Russia's advance has been very slow – about 1km (0.6 miles) in the past two weeks. Mr Mashovets also said Moscow recently relocated new units from the Donbas – to Sumy region.
Colonel Vadym Mysnyk, a spokesperson for a formation of the ground forces that is involved in defending the Sumy region, said Russian forces mostly use small groups on motorbikes and buggies during their attacks.
The movement of larger armoured vehicles could be quickly spotted by drones and destroyed, Col Mysnyk explained. On the battlefield, speed and mobility are crucial.
But the Sumy region has regularly come under attack by Russian air strikes and artillery fire, with the regional administration reporting that since Saturday, Russia has dropped more than 30 guided bombs on the area.
One of the biggest attacks took place last month when ballistic missiles hit the city of Sumy killing 34 people. Several weeks later, drones hit an intercity bus killing nine people.
Russia targets residential buildings, hospitals and civilian vehicles to spread panic among the population, Col Mysnyk claimed. Russia denies that it targets civilians in strikes, saying they are aimed at military targets.
