Saudi Arabia says two of its oil tankers suffered “significant damage” in a “sabotage attack” early Sunday off the coast of the United Arab Emirates. No details, however, about the specifics of the damage were released. 

The kingdom’s energy minister said one of the tankers had been on its way to the Saudi port of Ras Tanura to pick up oil to deliver to the United States.

The United States issued a warning early Monday about alleged “acts of sabotage” aimed at ships off the United Arab Emirates coast. The warning comes at a time of heightened tensions between the U.S. and Iran. 

Earlier, the UAE said four commercial ships were subjected to “sabotage operations” Sunday near its territorial waters in the Gulf of Oman, but did not give any details on the sabotage or who owned the ships, other than saying they were of different nationalities.

They say no one was hurt and no chemicals or fuel were spilled from the ships. 

Iranian foreign ministry spokesman Abbas Mousavi said Monday in a statement that the attacks on the ships “are alarming and regrettable.” He called for an investigation into the attacks and gave a warning about “adventurism” by foreign players who want to disrupt maritime security. 

The UAE says international bodies are helping with the investigation.

“Carrying out acts of sabotage on commercial and civilian vessels and threatening the safety and lives of those aboard is a serious development,” the UAE foreign affairs ministry said Sunday, urging all nations to take their responsibilities to prevent actions by anyone looking to undermine maritime safety.