The investment community seems to be underestimating the potential fallout from rising tensions between the United States and Iran, CNBC's Jim Cramer warns.

Just after Monday's opening bell on Wall Street, Cramer said on "Squawk on the Street" that the key to the stock market is: "Gold, gold, gold," which was up for the ninth straight session.

"When I see this endless buying for gold it makes me think for the first time people are just saying, 'I'm really fearful,'" said Cramer. He pointed out that the gold buying started even before Thursday night's U.S. drone strike in Iraq that killed top Iranian commander Gen. Qasem Soleimani as he was leaving Baghdad's airport. Soleimani had been the leader of a special forces unit of Iran's Revolutionary Guard.

Often in times of international strife, investors buy gold and U.S. bonds as perceived safety from historically riskier investments such as stocks.

"It's not just Treasurys. The gold buying has been endless; over and over and over. It feels like gold wants to go to $1,700 to $1,800. Now that would be very negative for the [stock] market," Cramer added.

Gold, early Monday, briefly soared to more than six-year highs above $1,590 per ounce. It surged 1.5% to $1,552 in New York trading Friday, after the Pentagon confirmed the death of Soleimani, which prompted threats of retaliation from Iran.

Before the stock market opened for regular trading Monday, Dow futures were tumbling more than 100 points which carried through to the open, after the Dow Jones Industrial Average on Friday broke a two-session winning streak.

Cramer on Monday asked, rhetorically, "Why aren't the futures down more? They should be. I think they should be because we haven't see what promises to be retaliation?"

"I don't think Iran is a paper tiger," the "Mad Money" host said. "Do they not have to do something after all the bluster?"

Despite losses Friday and Monday, the Dow remained only about 1% away from Thursday's all-time highs, which had picked up where 2019's stellar 22% rise had left off.