European stocks were volatile on Tuesday, as signs emerged that a fragile ceasefire between the U.S. and Iran may be crumbling into renewed fighting.

By 03:25 ET (07:25 GMT), the pan-European Stoxx 600 had risen by 0.2%, the Dax in Germany had increased by 0.2%, and the CAC 40 in France had gained by 0.3% — all erasing slight initial drops at the start of trading. The FTSE 100 in the U.K. was the laggard, sliding by 1.0%.

The U.S. and Iran carried out a barrage of fresh attacks on Monday, as Tehran responded to President Donald Trump’s attempt to reopen shipping through the Strait of Hormuz, a vital waterway for roughly a fifth of the world’s oil.

Several merchant ships in the Gulf region reported fires or explosions. The U.S. also claimed it had successfully helped two American-flagged vessels transit the strait despite having to fight off attacks from Iranian drones and armed small boats.

The conflict also showed indications that it was once again spreading around the Middle East. In the United Arab Emirates, air defense systems engaged ballistic missiles and drones launched from Iran. An oil terminal in the city of Fujairah was also attacked.

For much of the more than two-month old war, the Strait of Hormuz has been effectively closed to tanker traffic due to the threat of Iranian strikes. Oil prices have shot up as a result, fueling fears of an inflationary spike that could weigh on global growth.

Brent crude futures, the global oil benchmark, last eased down by 0.8% to $113.56 a barrel, but remain well above pre-war levels.

Trump, who is facing increasing pressure over the war from some U.S. lawmakers, has offered few details on his plan to unblock the conduit, dubbed “Project Freedom,” while Iran’s foreign minister has warned the U.S. against being drawn into a “quagmire.”

In individual stocks, shares of HSBC slumped by more than 5% after the bank posted lower-than-anticipated first-quarter profit due largely to a surprise $400-million charge related to a fraud case in Britain.

Anheuser-Busch InBev, on the other hand, rose thanks to quarterly profit that topped estimates.