Daphne Caruana Galizia's three sons have also called for the country's prime minister to resign.

Caruana Galizia died in an explosion shortly after she left her home in Bidnija, near Mosta, on Monday.

She was known for her blog accusing top politicians of corruption.

A Facebook post by Matthew Caruana Galizia, signed by his brothers Andrew and Paul, said they had faced "unrelenting pressure" from Malta's leaders to "endorse a million-euro reward for evidence leading to the conviction of our mother's assassins".

But they said they are "not interested in justice without change".

"A government and a police force that failed our mother in life will also fail her in death. The people who for as long as we can remember sought to silence our mother cannot now be the ones to deliver justice," they said.

They took aim at Prime Minister Joseph Muscat and called for him to stand down. "Show political responsibility and resign. Resign for failing to uphold our fundamental freedoms," they said.

The sons demanded he replace Malta's police commissioner and attorney general "with public servants who won't be afraid to act on evidence against him and those he protects".

• Malta's anti-corruption warrior

After Caruana Galizia's death, Mr Muscat denounced the killing, calling it an attack "on the freedom of expression in our country".

Speaking to the BBC, he said the journalist was "a very harsh critic of mine" and described her killing as "a nightmare".

"I wouldn't know whether this is because of something she had written, or something she was going write," he said.

Daphne Caruana Galizia was a harsh critic of the government and effectively triggered an early election this year by publishing allegations linking Prime Minister Joseph Muscat to the Panama Papers scandal.

Mr Muscat and his wife denied claims they used secret offshore bank accounts to hide payments from Azerbaijan's ruling family - and he was returned to power in the election, despite the controversy.

Caruana Galizia's popular blog had also targeted opposition politicians, calling the country's political situation "desperate" in her final post.