The United States and Iran traded missile fire and accusations on Thursday as tensions in the Strait of Hormuz ratcheted up, threatening the cease-fire.

U.S. Central Command said in a statement that the United States had “intercepted unprovoked Iranian attacks and responded with self-defense strikes” while American guided-missile destroyers were transiting the strait to the Gulf of Oman on Thursday.

The statement said that Iranian forces had launched multiple missiles, drones and small boats as three U.S. Navy ships were transiting the strait. None of the naval vessels were hit, Central Command said.

Central Command “eliminated inbound threats and targeted Iranian military facilities responsible for attacking U.S. forces, including missile and drone launch sites; command and control locations; and intelligence, surveillance and reconnaissance nodes,” the statement said. Central Command “does not seek escalation but remains positioned and ready to protect American forces.”

Iran, for its part, accused the United States of launching “unprovoked” attacks as the ships transited the strait. Iran’s armed forces said that the U.S. military carried out airstrikes on Qeshm Island and two other cities on the country’s southern coast on Thursday. It also said that the U.S. Army had targeted an Iranian oil tanker heading toward the Strait of Hormuz.

Explosions were also heard in Tehran, Iran’s capital. The state news agency IRNA reported two large explosions in the western part of Tehran and the activation of air defenses. Several residents of the city also said in text messages that they woke up to the sounds of explosions that shook their homes, creating panic.

The escalating attacks raised the threat of a complete breakdown in the cease-fire, which had been in place since last month and had established weeks of relative calm in Tehran.

Farnaz Fassihi contributed reporting.