U.S. stock futures were steady and Treasury yields ticked higher after Brent crude oil briefly topped the $100 a barrel mark for the first time since July in early morning European trade.

American forces destroyed five Iranian oil tankers in response to attacks by Iran on U.S. warships, U.S. Central Command said, adding pressure to an already tight oil market. Shrinking storage levels and rising Chinese demand are biting as markets increasingly anticipate an indeterminate block to shipping through the Strait of Hormuz.

Brent crude oil contracts for November delivery were last 2% higher at $99.88 a barrel, while WTI rose 1.5% to $94.45 a barrel.

Despite oil passing the $100 mark, U.S. stock futures largely held firm after following Dow-led losses in the last session. Futures for the Dow Jones Industrial Average edged 0.1% lower, while S&P 500 futures were flat. Nasdaq futures added 0.15%.

Treasurys fell on the surge in Brent, with yields rising through the European morning. Yields on 10-year Treasurys rose by 1.5 basis points to 4.809%, while 30-year yields added 1.1 basis points to 5.259%. Eurozone bond yields also ticked higher ahead of the European Central Bank's policy decision Thursday.

Asian equity indexes were mixed as the Nikkei 225 slipped 0.2% while the Shanghai Composite added 0.3%. European stocks responded more negatively to higher Brent and natural gas prices, with the continent-wide Stoxx 600 dropping 0.5%.

"European indices are more vulnerable to changes in energy prices and the global economic outlook, as they are more cyclical than their international peers," Swissquote's Ipek Ozkardeskaya wrote in a research note.

In currency markets, the yen strengthened further against the dollar after Treasury Secretary Scott Bessent dared traders to bet against the Japanese currency.

"I am the house now," Bessent said at an event in Texas Tuesday, pointing out the Treasury's asymmetrical access to market-sensitive information. The greenback fell to its lowest level in nearly three weeks against a basket of currencies, and dropped 0.6% to 153.05 yen.

Bitcoin rose 1% to $79,249.20, though the cryptocurrency continued to find resistance at the $80,000 mark. Gold futures also nudged higher, rising 0.4% to $4,455.39 a troy ounce.

For the day ahead, the U.S. Treasury's increase in buybacks for longer-dated bonds will kick in.