TOKYO—The Bank of Japan kept up its relentless quest to defend a key yield cap by offering to buy unlimited amounts of 10-year government bonds on Tuesday, underscoring its resolve to keep policy ultra-loose and putting downward pressure on the yen. The BOJ’s intervention raised the stakes for policymakers in the world’s third-largest economy as Japan tries to navigate the rising cost of imports from a weakening currency and global fallout of the Ukraine war. The bond market intervention is in line with an announcement the BOJ made on Monday to offer unlimited bond buying from Tuesday to Thursday to keep the 10-year Japanese government bond (JGB) yield from rising above an implicit 0.25 percent cap it sets around its 0 percent target. The BOJ made two offers on Tuesday, after the first in the morning failed to push down yields much. Combined, the offers drew bids worth 528.6 billion …