Japan's Government Pension Investment Fund (GPIF), the world's largest pension fund, has suspended stock lending for short selling, calling the practice inconsistent with its responsibilities as a long-term investor.

The move, announced by the GPIF on Tuesday, is a blow for short sellers, who rely on securities lending to bet against companies and who are facing renewed moves in a number of countries to curb their activities.

"The current stock lending scheme lacks transparency in terms of who is the ultimate borrower and for what purpose they are borrowing," the GPIF said on its website.

Short sellers borrow shares and immediately sell them, betting the price will fall before they buy back the shares and return them, pocketing the difference.

Advocates see them as a healthy counterbalance to investor over-confidence and corporate spin. Critics argue they are destabilizing because they have an incentive to drive down a company's share price.

Elon Musk, the chief executive of Tesla, a popular target for short sellers, was quick to applaud the GPIF's move.

"Bravo, right thing to do! Short selling should be illegal," the high tech entrepreneur said in a tweet.

Musk has previously criticized fund managers for lending shares for hedge funds to short, saying the fund firms made "excessive profit" from the practice.

Securities lending has emerged as small but significant source of extra returns for funds. BlackRock, the world’s largest asset manager, reported total securities lending revenue of $597 million in 2017, compared with $579 million in 2016, according to a securities filing.

GPIF, which manages 160 trillion yen ($1.47 trillion) of assets, said it will continue to lend debt securities and may reconsider the halt to stock lending if it sees an improvement in transparency.

In the July-September quarter, GPIF reported a profit of 1.8 trillion yen. Amid Japan's ultra-low interest rates, the fund, which is closely watched by global investors, has retreated from unprofitable domestic bonds in favor of foreign assets.