HAVANA (AP) – Fidel Castro made a surprise stop outside the US Interests Section Wednesday night, but would not say what kind of construction project he is directing outside the mission that is increasingly becoming a flash point for bad US-Cuba relations.

Dressed in his olive green uniform and surrounded by security men, Castro made the nighttime visit one day after directing a massive march past the building to protest recent US actions aimed at Cuba, including a new electronic sign streaming news and human rights messages.

“If I tell you, it will ruin the surprise,” Castro told reporters, who asked what the workers were building outside the mission. The Cuban president said he was there primarily “to greet the workers.”

Earlier Wednesday, government construction workers said they were expanding the open-air Anti-Imperialist Plaza, which sits directly in front of the mission on Havana’s Malecon coastal highway.

Workers started drilling and transporting materials early in the morning, closing down several streets around the site.

The American mission said in a statement that it was informed by the Cuban government after the march Tuesday that the parking lot in front of the building could no longer be used until further notice.

“The regime appears to be building a permanent structure that, we believe, seeks to obstruct Cubans’ view of the uncensored messages and information posted on our streaming billboard,” the US statement said. “The regime’s reaction is not surprising: building walls to isolate Cubans from the rest of the world is what the regime knows best.

“Why cannot the regime allow Cubans to make up their own minds as to what they want to think, read and say publicly?”

The plaza includes a stage used for music concerts and political events attended by Castro and other Communist Party leaders.

The American mission irked Castro last week when it installed the electronic sign on the facade of its main building with streaming text of sayings about freedom and excerpts from the Universal Declaration of Human Rights, to which Cuba is a signatory.

Castro characterised the new US messages as “provocations” and said they appeared to be aimed at breaking off the limited contact between the two governments, which have been without diplomatic relations for 45 years.

The US has an interests section under the Swiss Embassy in Havana to handle consular affairs such as visa processing. Cuba has a similar office in Washington.