Tehran has tried to exert control over the Strait of Hormuz since the US and Israel launched strikes against Iran on February 28. It has restricted passage through the waterway, which carried about a fifth of global oil and liquefied natural gas trade before the war, in an effort to gain leverage over Washington.
Its threats and attacks have severely curtailed traffic through the strait, driving up oil prices.
The two officials declined to provide details of the new strategy, but one said Iran had started using different offensive tactics against vessels it considered in violation of its restrictions about 10 days ago, adding that this had led to an increase in attacks on such ships.
The strategy included a change in the type as well as the pace of attacks, with one goal being to influence the outcome of the US vote, they said.
"The aim is to frustrate efforts by the United States and its allies to bring down global oil prices," one of the two officials said.
The decision to adopt the new strategy had been taken at the highest levels of Iran's leadership and was fully coordinated across the country's ruling system, the officials said.
A US military official, speaking on condition of anonymity, confirmed Iran had changed tactics in one significant way: after the US destroyed much of Iran's radar capabilities, Iran's Islamic Revolutionary Guard Corps (IRGC) had started using unarmed spotters in small boats to identify potential targets, including US naval vessels, the official said.
Last week, in a previously unreported incident, the US military determined that Iranian spotters were operating from a dhow, calling in targets to the IRGC, the official said. US forces confronted the vessel, told its occupants to abandon ship and then destroyed it. There were no casualties, the US official said.
The war - and its $US3 billion monthly price tag - has become a key issue on the US campaign trail for November's midterm elections, which will decide control of Congress.
US President Donald Trump has been weighing next steps against Iran, but has said he will not attack again before the vote.
The US has meanwhile been pressing its own naval blockade of Iranian ports and extending sanctions as it tries to pile economic pressure on Tehran to reach a deal to end the conflict.
The standoff over Hormuz has left global energy markets exposed to further disruption, with the threat of attacks and high shipping and insurance costs complicating efforts to restore normal traffic.
As part of the new strategy, Tehran will also expand the geographical scope of its operations beyond the Strait of Hormuz to the Gulf of Oman and waters further afield, the officials said.
The second Iranian official added Tehran would not allow Trump to bring down oil prices before the November elections.
"Just when they think they are getting close to the point where prices will fall, we will push them away from it. This is a game of chess," the second official said.
"Such vessels would be safe nowhere, even outside the Strait of Hormuz."
The Pentagon and Iran's Foreign Ministry did not immediately respond to requests for comment.
Both Iranian officials said Tehran is moving towards a situation in which no vessel violating its restrictions would be able to pass through the strait.
"It will be complete closure soon," one of the officials said.
