Russia is reportedly preparing to hold referendums in parts of southern Ukraine under its control with an eye on annexation. But observers suggest it will be difficult to hold referendums in September as scheduled.

Russia is said to be preparing to hold referendums on the annexation of the Kherson and Zaporizhzhia regions on September 11 to coincide with local elections in Russia.

A senior official at the intelligence agency of Ukraine's defense ministry told media on Friday that preparations are almost complete with politicians and volunteers arriving in the Russian-controlled regions.

However, the US-based think tank Institute for the Study of War says Ukraine is fighting back in those regions, and that there is also friction within the occupation administrations and not enough collaborators to oversee the referendums.

The institute says Russia's "sham referenda" on the annexation of southern Ukraine will unlikely succeed.

Meanwhile, the governor of Ukraine's southeastern Zaporizhzhia region took to social media on Saturday and criticized Russia's shelling of an apartment building that killed five people, including two children aged 2 and 8.

On Friday, Ukrainian forces said on social media that they had destroyed two bridges in the southern Kherson region that served as supply routes for Russian-occupied territory.