New Delhi, March 27 -- Iran appears to be setting itself up as the gatekeeper for the Strait of Hormuz, the world's most important artery for oil shipments. The move could cement Tehran's de facto chokehold over the crucial waterway and formalize its ability to keep its own oil flowing to China.

Iranian communications to the United Nations maritime authority and the experience of ships transiting the strait suggest the creation of something akin to a "toll booth." Ships must enter Iranian waters and be vetted by Iran's Islamic Revolutionary Guards Corps. At least two vessels have paid for passage.

Traffic through the strait has fallen by 90% since the start of the Iran war, sending global oil prices skyrocketing and inflicting alarming ...