The pound's rally to a four-month high against the dollar is proving too much for currency traders unsure whether Mark Carney will step up stimulus efforts when he takes over as Bank of England (BOE) governor next month.

Sterling's failure to extend its advance after rising above its 200-day moving average on June 13 may be a signal its winning streak is ending, according to Barclays Plc. The pound is also approaching a key Fibonacci retracement level where sell orders tend to be clustered, while the stochastic oscillator crossed a threshold that implies an imminent reversal.

“We're at a point where sterling is a bit stretched,” Ken Dickson, an Edinburgh-based director for foreign exchange at Standard Life Investments Ltd., which oversees about $281 billion, said in a phone interview on June 17. “It could be pretty difficult to get beyond here in the near term.”