Iranian crude prices have climbed as fewer cargoes reach Chinese buyers under a tightening US blockade, Reuters reports.

Traders said Iranian oil deliveries for September and October had fallen below volumes in July and August. Sellers have already placed much of the crude shipped earlier, leaving fewer barrels available.

Iranian oil that traders offered at discounts is now commanding premiums as supplies tighten.

The shift follows a decline in Iranian exports since mid-July, when the United States intensified its blockade on the country’s oil shipments.

Pressure on buyers could increase after US President Donald Trump threatened secondary sanctions on Thursday against countries that continue trading with Iran.

China remains the largest destination for Iranian crude despite years of US sanctions.