LONDON (Reuters) - It is important Britain continues to show it is supporting Ukraine for the long haul, Prime Minister Boris Johnson said on Saturday, warning of a risk of "Ukraine fatigue" as the war drags on.

"The Russians are grinding forward inch by inch and it is vital for us to show what we know to be true which is that Ukraine can win and will win," Johnson told reporters on his arrival back in Britain from a visit to Kyiv.

Some members of his Conservative Party had criticised him for making the trip instead of attending a conference in northern England.

"When Ukraine fatigue is setting in, it is very important to show that we are with them for the long haul and we are giving them the strategic resilience that they need," Johnson said.