The sister of murdered journalist Daphne Caruana Galizia was involved in a tense stand-off with Maltese police on Tuesday after a group of protesters stormed into the prime minister’s office in Valletta, the capital, to demand his immediate resignation.

The 30 protesters were trapped inside the prime minister's office, an imposing stone palace built by the Knights of Malta 500 years ago, after police and soldiers locked the doors.

Corinne Vella, Mrs Caruana Galizia’s sister and an outspoken critic of the government, banged on the green wooden doors, demanding that journalists be allowed to see the protest inside. The protesters could be heard blowing whistles and banging drums.

“You should not be blocking access to a public property where protesters are demanding justice for a murdered journalist,” Ms Vella told the police officer in charge of the operation.

The police superintendent, who refused to give his name, said the protesters had breached “security measures”.