International crude oil prices rose on August 18 as concerns mounted over energy supplies from the Middle East. By 12 a.m. Greenwich Mean Time, Brent crude had gained 27 cents, or 0.3 percent, to $91.14 a barrel. US West Texas Intermediate crude rose 42 cents to $85.04 a barrel.

The increase followed fading prospects for an agreement between Iran and the United States to extend a ceasefire. Tensions in the region increased after Tehran announced it would take a more aggressive stance. Washington also ruled out the possibility of extending the ceasefire, raising concerns that conflict between the two countries could intensify again.

Earlier in the day, WTI had risen by more than 1 percent to $85.37 a barrel. In the previous session, Brent reached its highest level since late July. Market participants fear that a major disruption to oil supplies from the Middle East could push international crude prices higher.