The Bank of Japan has probably finished buying exchange-traded funds this year, according to Amundi Japan Ltd., signaling the removal of a key support for the nation's equities amid a global selloff.

The central bank didn't add to ETF holdings Wednesday even as the Topix index tumbled 2 percent for its largest drop since Nov. 17. The BOJ is about ¥26.6 billion short of its ¥3.8 trillion forecast for the end of 2014, while it has been recently buying in blocks of ¥37.4 billion. As another purchase of that size would put it above its target, the bank is likely to refrain from further investments in 2014, according to Akio Yoshino, chief economist at Amundi Japan.

"The BOJ has been buying the same amount of ETFs each time to dispel views that it's acting arbitrarily and to curtail impact on the market," Yoshino said by phone from Tokyo Thursday. "I'd say it didn't buy yesterday because it's pretty much reached the ¥3.8 trillion level."