Yemen’s Iran-backed Houthi rebels launched a wave of attacks on Saudi Arabia on Tuesday, wounding more than 70 people and sparking fires at oil facilities and other infrastructure, according to authorities.

The attacks mark a major escalation in renewed hostilities between Saudi Arabia, a key U.S. ally in the Middle East, and the Houthi movement.

The latest violence is also raising concerns about further instability in a region already strained by years of conflict, as well as potential consequences for global energy supplies.

Recent clashes have increased pressure on already constrained oil markets, with the Houthis targeting infrastructure linked to a shipping corridor Saudi Arabia has relied on to move crude to international markets while traffic through the Strait of Hormuz remains restricted amid the U.S.-Iran war.

Tuesday’s attacks struck Saudi oil facilities connected to the alternative route through the Bab el-Mandeb, a strategically important waterway off the southern Arabian Peninsula connecting the Red Sea with the Gulf of Aden.

The renewed fighting has also heightened fears of a broader return to war in Yemen.

The conflict between Saudi Arabia and the Houthis dates back more than a decade. Yemen’s civil war began in 2014 when the Houthis seized the capital, Sanaa, and large parts of northern Yemen, forcing the internationally recognized government into exile.

A Saudi-led coalition intervened militarily the following year in an effort to restore the government.

The latest escalation threatens to deepen regional tensions and create further risks for international shipping and energy markets along some of the world’s most strategically important maritime routes.