US equity indexes were mixed in Monday's midday trading, with technology topping sector charts and helping lift the Nasdaq Composite.

The Nasdaq rose 0.4% to 23,000.3, while the S&P 500 climbed 0.2% to 6,831.2. Both gauges traded lower earlier in the session. The Dow Jones Industrial Average, however, fell 0.2% to 47,810.6.

Defensive sectors -- consumer staples and utilities -- led the decliners.

The US military blockade on all traffic entering and leaving Iranian ports started at 10 a.m. ET Monday, after weekend peace talks in Pakistan faltered, CNN reported Monday.

"If any of these ships [that the president refers to as Iran's 'fast attack ships'] come anywhere close to our BLOCKADE, they will be immediately ELIMINATED," Trump said on a social media post.

In company news, Goldman Sachs (GS), which reported higher Q1 earnings and net revenue pre-bell, is launching a new three-tranche offering in the US investment-grade debt market, with bond maturities spanning four to eight years, Bloomberg said Monday, citing a person with direct knowledge of the matter.

Shares of the investment bank dropped 2.5% intraday, the steepest decline on the Dow.