CAIRO — Iran said Sunday it struck an unmanned U.S. vessel trying to enter the Strait of Hormuz, the latest salvo in a new flare-up of fighting between the two countries. The U.S. did not immediately confirm the purported attack, which came a day after the U.S. military said forces struck three Iranian oil tankers in response to a missile attack on Navy warships. The war began with U.S. and Israeli attacks on Iran on Feb. 28. But since a ceasefire agreement was announced in June, on-and-off fighting has persisted with both sides trying to inflict military and economic pain as negotiations have collapsed. Strikes come about a week after fighting resumed The U.S. and Iran resumed attacks last week, following a month of relative calm, with the Strait of Hormuz and Iranian communities along it again being targeted. At least five people were killed earlier in the week during a U.S. bombardment of southern Iran. The Trump administration appears to have adopted a dual-prong approach to the conflict, responding militarily to attacks on the strait while going after foreign financial institutions