LONDON—Oil prices extended gains on Thursday after the OPEC+ alliance of producers stuck to its reduced output policy and U.S. crude stocks fell, with optimism over a new U.S. pandemic relief bill adding further price support. Brent crude futures gained 24 cents, or 0.41 percent, to $58.70 a barrel by 1346 GMT, having earlier hit their highest level since Feb. 21 last year at $59.04. U.S. West Texas Intermediate (WTI) crude futures climbed 32 cents, or 0.57 percent, to $56.01 after reaching its highest settlement level in a year on Wednesday at $55.69. “Supporting factors outweigh negative developments at the moment,” said PVM Oil Associates analyst Tamas Varga, citing high compliance with OPEC+ production cuts and its declared target to accelerate stock depletion. “The extra 1 million barrel per day (bpd) Saudi cuts that started this month imply further stock draws until at least the end of the first quarter,” …