King Charles will resume public engagements next week after making encouraging progress in his cancer treatment, Buckingham Palace has said.

It won’t yet be a full return to official engagements for the King, but the palace is sending positive signals.

The King will begin next Tuesday with a symbolic trip to a cancer treatment centre.

His summer plans include a state visit, where he will host the Emperor and Empress of Japan.

In the coming weeks, the palace said, he would undertake more external engagements.

The King is said to be “greatly encouraged” to be going back to more public events.

It’s a message of cautious optimism, but the King’s treatment – which began in February – is still continuing and there is no date given for its conclusion.

Buckingham Palace gave the update on the King’s return to public-facing duties and his condition in a statement released on Friday.

“It is too early to say” for how much longer his treatment will continue, the palace said.

It added that doctors were “very encouraged by the progress made so far and remain positive about the King’s continued recovery”.

The type of cancer has not been disclosed, but the King’s medical team are “sufficiently pleased with the progress made so far that the King is now able to resume a number of public-facing duties”.

A picture of the King and Queen Camilla, taken earlier this month in the gardens of Buckingham Palace, has also been released.

It remains uncertain if he will be attending some of the big events coming up in the calendar, such as Trooping the Colour, the D-Day commemorations, summer garden parties, Royal Ascot, and overseas trips in the autumn.

Decisions will be made according to medical advice nearer the time, says the palace.

But it added that it would not be a “full summer programme”.

The King has missed customary royal public engagements since a procedure for an enlarged prostate and his subsequent cancer diagnosis announced in February,

Next week’s trip to a cancer treatment centre will be made with Queen Camilla, and he will meet patients and staff and show his support for cancer research. It is not where he is receiving treatment.

Although he has been carrying out his private work as head of state, including the regular meetings with the prime minister, this visit will be his first official public engagement this year.

At an Easter Sunday church service in Windsor, he surprised the crowds by greeting well-wishers and shaking people’s hands.

In late June, the King will receive the Emperor and Empress of Japan in his role as head of state – the first official state visit by Japan since 1998.

The highlights of such visits usually include a state banquet at Buckingham Palace and a carriage parade, but there could be adaptations for this visit, depending on the King’s condition.

The Royal Family has had a difficult start to the year, with the Princess of Wales also undergoing treatment for cancer.

They have also faced intense public scrutiny and social media speculation, and the palace will hope this more positive news draws a line under what has been a rocky time for the royals.

Since his cancer diagnosis, the King has spoken of how moved he has been by all the messages and cards wishing him a good recovery, particularly seeming to enjoy some of the funnier cards.

On Friday, Buckingham Palace said the King and Queen “remain deeply grateful for the many kindnesses and good wishes they have received from around the world throughout the joys and challenges of the past year”.