Mizuho Securities, the brokerage arm of Mizuho Financial Group, "has room for further growth" in the United States and acquisitions are one option it is exploring, CEO Yoshiro Hamamoto has said.

Its U.S. business, which is mainly investment banking and trading, accounts for roughly a third of the Japanese brokerage's profit.

It was also the highest ranked Asian firm in U.S. investment banking league tables for the first half of this year, coming 12th for both equity and debt underwriting and 18th for merger-and-acquisition advisory, according to Refinitiv data.

Hamamoto said in an interview that target firms or potential partners could be research companies, asset managers or boutique investment banks with strengths in specific sectors.

In some industry sectors such as health care, Mizuho wants to extend coverage with more bankers, he said.

"It doesn't have to be a merger, it could be a business alliance," Hamamoto added.

This year, the Mizuho group acquired Capstone Partners, a Dallas, Texas-based private equity placement agent that helps private equity firms find limited partners to invest in their funds.

Hamamoto also said the brokerage plans to bolster its business of connecting global investors with Japanese startups, which have drawn interest in recent years.

Despite global market headwinds, funds raised by Japanese startups in the first six months of the year jumped 11% from a year earlier to more than ¥400 billion ($3 billion), according to data provider INITIAL.

"The Japanese startup segment used to be small with just some certain domestic investors involved, but that's changing," Hamamoto said.