The United States has armed its warplanes with "bunker-busting" bombs, a move seen as a message to Iran, according to a report by The Wall Street Journal.

Citing anonymous US officials, the report states that the US has started equipping its B-52 bombers with the 5,000-pound GBU-28 bombs, which are designed to penetrate hardened underground facilities, including those believed to be used by Iran's nuclear program.

The move comes amid escalating tensions between the US and Iran, with both sides engaging in a war of words over the latter's nuclear program and alleged support for regional militias.

The US has repeatedly accused Iran of trying to develop nuclear weapons, a charge Tehran denies. The 2015 nuclear deal between Iran and world powers, which lifted economic sanctions in exchange for curbs on Iran's nuclear program, has been on the brink of collapse since former President Donald Trump unilaterally withdrew the US from the agreement in 2018.

The Biden administration has expressed its willingness to rejoin the deal if Iran returns to compliance, but negotiations have stalled as both sides refuse to budge on key issues.

The arming of the warplanes with bunker-busting bombs is seen as a signal to Iran that the US is prepared to take military action if necessary. The move is also likely to be viewed with concern by other countries in the region, including Israel and Saudi Arabia, which have long pushed for a more aggressive stance towards Iran.