The United States called Wednesday for two Iranian ships in the Mediterranean Sea to adhere to international law and said it was keeping a careful eye on their activities.

Iranian vessels crossed the Suez Canal for the first time since the 1979 Islamic Revolution, when relations between Tehran and Cairo nosedived. The ships have alarmed nearby Israel, the arch-foe of Iran's Islamic regime.

"We are watching the situation," said Colonel Dave Lapan, a Pentagon spokesman.

"We have said generally that Iran's actions are not helpful, but we would expect that these Iranian ships would adhere to international law no matter where they operate," Lapan said.

Asked about reports that the vessels were heading to Syria, Iran's main Arab ally, Lapan voiced hope that the ships were "adhering to international law and not engaging in activities that are threatening of security."

The US military knows "that they have transited the Suez Canal, but we don't know why or what it is they're planning to do," he said.

Israel has put its navy on alert. Israeli President Shimon Peres said on a visit to Spain that the warships' crossing was a "political provocation."