The United States significantly widened its military campaign against Iran on Friday, striking bridges, energy facilities and a key port, according to reporting from the Guardian. The expanded strikes prompted swift retaliation from Tehran, which launched attacks against U.S. allies in the Middle East.

U.S. airstrikes hit bridges in Iran’s southern Hormozgan province, killing at least seven people, Iranian state TV reported. The bridges served as a key transit point for Bandar Abbas, Iran’s main port, raising the prospect of significant disruption to the country’s shipping and trade.

Further American strikes brought down a tower at Chabahar port on the Gulf of Oman and targeted key electrical infrastructure as well as Iranshahr airport, according to the Guardian. Iran said the latest attacks struck civilian infrastructure.

The U.S. military rejected those claims. According to the BBC, the U.S. said its attacks were intended to ‘further degrade Iranian military capabilities’ and denied targeting civilian sites.

In response to the American campaign, Iran expanded its own attacks to hit U.S. allies in the region, including Syria and Bahrain, as reported by CNBC. The tit-for-tat strikes mark a sharp intensification of hostilities between the two countries.

The escalating standoff comes as a fragile truce signed by the U.S. and Iran last month showed further signs of unravelling, according to CNBC. The renewed exchange of strikes suggests the agreement is failing to hold.