Ukraine's security service said Monday it had detained an informer accused of helping Russia plot an attack on President Volodymyr Zelensky as he visited a flood-hit region.

The SBU security service said the detained woman was gathering intelligence to try to find out Zelensky's itinerary ahead of his visit to the southern Mykolaiv region.

It published a blurred image of the woman being detained by masked officers in a kitchen, as well as some phone messages and handwritten notes about military activity.

Ukraine regularly accuses local residents who support Russia of passing information to help Moscow's military.

Zelensky said on Telegram Monday that the head of the SBU had updated him about the "fight against traitors".

Zelensky visited the Mykolaiv region in June after it was hit by flooding caused by the Kakhovka dam breach and in July after shelling.

The SBU said that Ukraine was aware of the plot ahead of time and put in additional security measures during Zelensky's visit.

It alleged the suspect was helping Russia prepare a "massive air strike on the Mykolaiv region".

She was allegedly seeking data on the location of electronic warfare systems and warehouses with ammunition.

The SBU said its officers kept monitoring the suspect to get more information on her Russian handlers and her assignments.

Officers then caught the woman "red-handed" as she attempted to pass intelligence data to Russian secret services, the SBU said.

It said the woman lived in the small southern town of Ochakiv in the Mykolaiv region and formerly worked in a store at a military base there.

She allegedly photographed locations and tried to get information from personal contacts in the area.

She may face a charge of unauthorised dissemination of information about the movements of weapons and troops.

If convicted, she could serve up to 12 years in prison.