President Trump, in a sudden reversal, announced on Tuesday that the United States would pause its efforts to help guide ships through the Strait of Hormuz, which Iran has effectively blocked for weeks.

Mr. Trump said the pause of an operation he had dubbed “Project Freedom” would last “for a short period of time.”

Though a few ships have made it through the strait, the initiative and reports of Iranian attacks have tested the four-week-old cease-fire, and experts have questioned how many companies would try to move through the strait with U.S. help.

Mr. Trump had given few details about the operation and much remained uncertain after he suspended it. Here’s a look at what we know, and what we do not.

What is ‘Project Freedom’?

Iran has effectively blocked most commerce through the vital shipping route at the mouth of the Persian Gulf. Some 1,600 ships are believed to be stranded. The U.S. Navy has also imposed a blockade on ships going to or from Iran.

Mr. Trump said in a social media post on Sunday that the United States would guide ships “safely out of these restricted Waterways,” which he described as a “humanitarian gesture.” He warned that any interference would be dealt with “forcefully.”

He did not make clear what it would mean for the United States to “guide” ships.

U.S. Central Command subsequently indicated that it would coordinate safe traffic among the ships but not directly escort any through the strait.

Why did Mr. Trump pause the program?

Mr. Trump said in a social media post that it was “based on the request of Pakistan and other countries,” as well as the “tremendous military success” and “great progress” toward an agreement with Iran to end the war.

He added that the pause was “to see whether or not the agreement can be finalized and signed.”

Pakistan has acted as a mediator in talks between the United States and Iran, but the state of negotiations is unclear. Before Mr. Trump announced that the initiative would be suspended, he said that he did not like that Iranian officials “play games” by talking to him with “great respect” and then appearing on television to say they never did.

The president has also not compromised on his own blockade and said on Tuesday that the U.S. Navy would continue to prevent ships from going into or out of Iranian ports.

Had any ships exited the strait?

Only two ships were known to have passed through the waterway on Monday. None seem to have made the trip on Tuesday.

Before the war, around 130 vessels made the passage daily.

Maersk, the Danish shipping giant, said a U.S.-flagged vehicle carrier operated by one of its subsidiaries had gone through the strait under the protection of the U.S. military.

It was unclear what route the vessel took and how the U.S. Navy had helped its passage.

Is the cease-fire holding?

American officials have insisted that it is despite a number of attacks in recent days.

U.S. forces on Monday shot down cruise missiles and drones and destroyed six Iranian military speedboats that were threatening vessels that the U.S. Navy was guiding through the strait, according to U.S. Central Command.

The Emirati authorities blamed Iran for attacks on a major oil port and an oil tanker in the Strait of Hormuz that injured three people. They were the first such attacks in the Emirates since the truce began four weeks ago.

South Korea said a Korean cargo ship caught fire after an explosion in that area, although it did not say the vessel had been attacked.

Iran did not officially confirm or deny that it had resumed attacks. A senior Iranian military official denied that its boats had been sunk, state media reported.

Mohammad Bagher Ghalibaf, Iran’s top negotiator, warned in Tuesday of an escalation and accused the United States of violating the cease-fire in a social media post.

He added that American actions had endangered shipping through the strait.