A Malaysian court on Monday sentenced senior opposition lawmaker Rafizi Ramli to 18 months in jail for releasing a classified document on the controversial state fund 1Malaysia Development Berhad (1MDB).

"I am not shocked, sad, angry, afraid or anything. No such feeling. Just another day. Been like this. What doesn't kill you makes you stronger," said Rafizi, vice president of the People's Justice Party, in a tweet ahead of the sentencing.

The rights group Lawyers for Liberty described the sentence as excessive, saying that Rafizi had performed his parliamentary duties by keeping the government accountable.

"The conviction and sentence will create a dangerous chill on free speech and result in a more repressive, opaque and unaccountable government," said the statement.

The 1MDB fund, founded by Prime Minister Najib Razak, has been the center of a political scandal after the American daily "Wall Street Journal" suggested last year that $673 million (624 million euros) of the fund had been stashed in the premier's personal accounts.

Judicial authorities in several countries have since taken action against the 1MDB.

In January, Swiss prosecutors formally asked for assistance from Malaysian authorities in their investigation into the 1MDB. The US Justice Department announced in July that it planned to seize up to $1 billion in assets tied to the state fund.

However, Najib has denied his involvement in the alleged money laundering scheme involving 1MDB, saying the accusations are a ploy from opposition parties.

Following a probe, the attorney general later said the questionable funds in the premier's personal accounts had been a donation from Saudi Arabia.

The prime minister faces calls for his resignation, including from members within his own political party.

ls/msh (AP, dpa)