Sri Lanka, April 14 -- The standoff between the United States and Iran deepened Tuesday as the U.S. declared it had blockaded Iran's ports, Tehran threatened to strike targets across the region, and Pakistan said it was racing to bring the sides together for more talks.

Though last week's ceasefire appeared to hold, the showdown over the Strait of Hormuz risked reigniting hostilities and deepening the region-wide war's economic fallout.

Talks aimed at permanently ending the conflict - which began Feb. 28 with U.S. and Israeli strikes on Iran - failed to produce an agreement last weekend, though Pakistan has proposed hosting a second round in the coming days.

Two Pakistani officials, who spoke on condition of anonymity because they were...