The American military on Monday was implementing a blockade on all ships entering and exiting Iranian ports, with the escalation pushing oil prices higher and weighing on U.S. stocks.

President Donald Trump and the Pentagon said in separate social-media posts that the blockade would be starting at 10 a.m. Eastern time.

Brent crude recently was up 7% to around $102 a barrel, while West Texas Intermediate crude rose 7% to $104 a barrel. The U.S. stock-market benchmark S&P 500 rose 0.1%.

Trump’s blockade is an effort to put pressure on Iran after weekend talks in Pakistan failed to produce an agreement.

The failure of the talks was “not a shock,” said Tobin Marcus, head of U.S. politics and policy at Wolfe Research, in a note. Marcus added that Trump’s announcement of a blockade was “more of a surprise,” but he emphasized that it is limited compared with the U.S. president’s “more expansive initial framing” of the move.

The blockade is rattling markets, but stocks have only partly given back their gains from last week, which came as the U.S. and Iran agreed on a cease-fire set to last two weeks. This reflects an assessment by traders that the two sides for now are “not going right back to the worst-case scenarios of high-intensity war,” Marcus said.