US-Iran war, Aug. 18 -- Oil prices advanced on Tuesday as hopes of a deal to end the Middle East conflict weakened, with Iran signalling a more aggressive approach and the US ruling out an extension of the ceasefire. The developments heightened concerns over potential disruptions to energy supplies.

Brent crude futures rose 27 cents, or 0.3%, to $91.14 a barrel, after touching their highest level since July 30 in the previous session. US West Texas Intermediate (WTI) crude futures gained 42 cents to $85.04 a barrel, following an earlier rise of more than 1% to $85.37, its strongest level since July 31.

The memorandum cited by the US president was signed in June and, technically, expired on Monday.

However, Washington and Tehran remain ...