DUBAI, United Arab Emirates (AP) — An explosion rocked a ship off Saudi Arabia's port city of Jiddah on the Red Sea, authorities said Monday, without elaborating.

The kingdom did not immediately acknowledge the blast, which struck off a crucial port and distribution center for its oil trade.

Initial reports also offered no cause for the explosion, though it comes after a mine attack last month that damaged a tanker off Saudi Arabia that authorities blamed on Yemen's Houthi rebels.

The United Kingdom Marine Trade Operations, an organization under Britain's royal navy, said the blast happened Sunday, without elaborating. It urged ships in the area to exercise caution and said investigations were ongoing.

Dryad Global, a maritime intelligence firm, also reported the blast.

Saudi Arabia’s state-run media did not acknowledge the explosion. The U.S. Navy's 5th Fleet, which patrols the Mideast, did not immediately respond to a request for comment.

The coordinates offered by the UKMTO put the blast just southwest of the port near anchorage for ships in the area. At least two oil tankers were known to be in that area, according to the ship-tracking website MarineTraffic.com — the Desert Rose and Al Amal Al Saudi, or the Hope of Saudi. Owners for the ships could not be immediately reached.

The apparent explosion comes after a mine exploded and damaged a ship off Saudi Arabia last month. Another mysterious attack targeted a cargo ship off the small port city of Nishtun in Yemen’s far east earlier this month.

Yemen's Iranian-backed Houthi rebels have used sea mines before in their long war against a Saudi-led coalition. However, the Houthis have not commented last month's attack.

Dryad Global said if it was the Houthis behind Sunday's blast, it “would represent a fundamental shift in both targeting capabilities and intent."

The Red Sea is a vital shipping lane for both cargo and global energy supplies, making any mining of the area a danger not only to Saudi Arabia but to the rest of the world. Mines can enter the water and then be carried away by the currents, which change by the season in the Red Sea.

The Red Sea has been mined previously. In 1984, some 19 ships reported striking mines there, with only one ever being recovered and disarmed, the U.N. panel said.

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Follow Jon Gambrell on Twitter at www.twitter.com/jongambrellAP.