Alexander Manzyuk | Reuters Oil extended gains Thursday on signs of a prolonged U.S. blockade of Iranian exports and stalled nuclear negotiations, stoking fears that supplies will remain tight for longer. The gains come as Axios reported that U.S. President Donald Trump had rejected Tehran's proposal to reopen the Strait of Hormuz, signaling the naval blockade will remain in place until a broader nuclear agreement is reached.  June futures for international benchmark Brent crude rose 1.96% to $120 a barrel, while U.S. West Texas Intermediate added 0.2% to $107.09. Stock Chart Icon Stock chart icon Brent oil prices Brent crude had risen about 6% on Wednesday and WTI gained 7%, as The Wall Street Journal reported, citing U.S. officials, that Trump had instructed aides to prepare for an extended blockade of Iran. Trump appeared to threaten Iran in a Truth Social post on Wednesday , saying the country "better get smart soon!" "Iran can't get their act together. They don't know how to sign a nonnuclear deal.…