SHIZUOKA, Japan--Bank of Japan Deputy Gov. Hiroshi Nakaso said Wednesday that the recovery in the country's exports has been "sluggish" and slow by historical standards, highlighting how lackluster shipments abroad have become a major debate topic among central bankers.

"While domestic demand remains firm, exports have recently been sluggish," Mr. Nakaso said in a speech to business leaders in the city of Shizuoka, central Japan.

Slow growth in emerging economies, a dip in U.S. demand due to unusually cold winter weather, and strong demand for goods at home before a sales tax increase in early April are among the reasons for Japan's poor export performance, Mr. Nakaso said. "However, even taking these factors into account, the pace of recovery in Japan's exports has been slower than in the past," given the support they are getting from the yen's weakness and an overall global economic recovery, he said.

The remarks by the career BOJ official seen as Gov Haruhiko Kuroda's right-hand man likely represent the mainstream view of the central bank's nine policy board members.

While the factors weighing down exports are expected to disappear gradually, "since exports as a whole have yet to pick up, continued attention without undue optimism is warranted," Mr. Nakaso also said.

But in a sign that a lack of vigor in exports is unlikely to spur the BOJ to act soon, Mr. Nakaso said that Japan is steadily pulling out of over a decade of deflation and is on track to see 2% inflation in next year or so. The economic impact of the increase in the sales tax rate to 8% from 5% on April 1 has been within the BOJ's expectations, he added.

Write to Takashi Nakamichi at takashi.nakamichi@wsj.com

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