Pressure is mounting on Malaysian Prime Minister Najib Razak, with lawmakers demanding he go on leave and be held accountable after U.S. officials initiated action to seize more than $1 billion they say was stolen from a state investment fund by people close to the premier.

That fund, known as 1MDB, was created in 2009 by Najib to promote economic development projects. Instead, U.S. prosecutors said, fund officials diverted more than $3.5 billion through a web of shell companies and bank accounts abroad.

Opposition lawmaker Wan Azizah Wan Ismail says Najib must give a full explanation in Parliament, and go on leave to ensure a full and transparent probe. Lawmaker Lim Kit Siang warned Thursday that Malaysia was "careening down the slope to becoming a failed, rogue state."