At least six Russian regions on the border with Ukraine raised terrorist threat levels Monday in all or parts of their territories as Russia’s invasion of Ukraine enters its seventh week.Local residents have reported a series of explosions in recent days that officials referred to as “incidents.”The Kursk region was the first to raise its terrorist threat level Sunday, citing “possible provocations” in an area that is used as one of several staging grounds for Moscow’s invasion of its neighbor.The authorities said security patrols will be increased and there will be military and police checkpoints. Analysts widely expect Russia to launch a major offensive in eastern Ukraine in the coming days, after military units were pulled back from around the Ukrainian capital. Following Kursk, the Belgorod, Voronezh and Bryansk regions elevated threat levels to “yellow,” the second-highest in a three-tier system.The Belgorod region also banned firecrackers and fireworks for two weeks “so as not to frighten people with unnecessary loud sounds,” governor Vyacheslav Gladkov said.

The Krasnodar region raised the threat level in two of its districts on the Ukrainian border.Annexed Crimea did the same in seven of its districts.

The Rostov region on the border with Ukraine’s separatist Donetsk and Luhansk republics was the only Russian border region not to raise its threat level in the past 48 hours.

Russia has grounded all flights to and from 11 airports in southern and central parts of the country since President Vladimir Putin ordered troops into Ukraine.