Update: Malta appeals for outside help to investigate car bomb death of journalist

Latest: Malta has appealed to the FBI and to European forensic experts to help investigate the car bomb death of the country's leading investigative journalist.

Update 3.37pm: Malta has appealed to the FBI and to European forensic experts to help investigate the car bomb death of the country's leading investigative journalist.

In her crusade against corruption, Daphne Caruana Galizia, 53, took on top politicians and other powerful Maltese, including by exposing links through the Panama Papers leak.

Ordinary Maltese called for a strike to demand that whoever was behind Monday's bombing be found and brought to justice.

Graffiti quoting the last words she wrote: "There are crooks everywhere you look" popped up on the island on Tuesday.

Some EU politicians are pressing for closer scrutiny of the tiny European Union nation in the Mediterranean Sea, which is considered a banking haven.

Earlier: A Maltese investigative journalist who exposed the island nation's links to offshore tax havens through the leaked Panama Papers has been killed as a bomb exploded in her car.

Daphne Caruana Galizia, 53, had just driven away from her home in Mosta, a large town on Malta's main island, when the bomb went off, sending the vehicle's wreckage spiralling over a wall and into a field, prime minister Joseph Muscat said.

He acknowledged she was "one of my harshest critics, on a political and personal level", but denounced the "barbaric attack" as "unacceptable" violence that also assaulted freedom of expression.

One of the topics the veteran reporter examined was what the documents from the 2016 leak said about Malta.

She wrote that Mr Muscat's wife, the country's energy minister and the government's chief-of-staff had offshore holdings in Panama to receive money from Azerbaijan.

Mr Muscat and his wife Michelle denied having companies in Panama.

Ms Caruana Galizia filed a police report two weeks ago saying she was receiving threats, police told Maltese news outlets on Monday.

She had been a regular columnist for the Malta Independent, writing twice weekly for the newspaper since 1996. She also wrote a blog called Running Commentary, which was followed by many in Malta.

Half an hour before she was killed, she posted to her website an item about a libel claim the prime minister's chief of staff had brought against a former opposition figure over comments the latter made about corruption.

Ms Caruana Galizia had been sued for libel over articles she wrote for her blog. Opposition leader Adrian Delia sued her over a series of stories linking him to a prostitution racket in London, and economy minister Chris Cardona claimed libel when she wrote that he visited a brothel while in Germany on government business.

Monday evening's parliamentary session was scrapped, except for briefings about the bombing given by Mr Muscat and Mr Delia, who called the reporter's killing a "political murder".

Mr Muscat said he had asked the US government and the FBI for help investigating the car bombing.

Ms Caruana Galizia is survived by her husband and three sons. One son, Matthew, was on the International Consortium of Investigative Journalists team that won the Pulitzer Prize for its work on the Panama Papers scandal.

The leak exposed the identities of rich and powerful people around the world who allegedly had offshore holdings in Panama.

Ms Caruana Galizia's family has asked the Courts of Malta to have the magistrate assigned to conduct the inquiry into the journalist's death replaced.

The family said the magistrate, Consuelo Scerri Herrera, "in her personal capacity, had launched judicial procedures against (Caruana Galizia) regarding comments she had written".

Ms Caruana Galizia for many years was a harsh critic of Malta's Labour party and government. More recently she had expanded her criticism to include the opposition Nationalist Party.

Her murder drew swift denunciations in the tiny EU nation.

"Daphne played a vitally important role in unearthing serious allegations of money laundering and corruption in Malta, including those involving senior figures in the Maltese government," said Sven Giegold, a Greens member in the European Parliament.

Italian news weekly L'Espresso, which has also written about alleged corruption linked to Malta, said the murder demonstrated that a well-documented expose "is perceived as a danger by the powerful and by organised crime".

European Parliament president Antonio Tajani called the development a "tragic example of a journalist who sacrificed her life to search for the truth".

AP