DUBAI- Qatar National Bank QNBK.QA said on Wednesday it had secured a $3.5 billion three-year syndicated loan for general corporate purposes, one of the first such deals by a Qatari government-owned firm since a regional diplomatic crisis erupted.

The syndication, which comprised 21 international banks, comes as QNB seeks to secure new funding lines in the wake of a dispute between Qatar and Saudi Arabia, the United Arab Emirates, Bahrain and Egypt.

QNB said it had already repaid in full an earlier $3 bln syndicated loan. That facility, which matured this year, was originally signed in 2015.

The loan to refinance the previous debt was increased to $3.5 billion due to strong demand from the market, it said.

The deal was "a reflection of the strong demand by the top tier global banks that want to continue to partner with QNB," said chief executive Ali al-Kuwari.

QNB said the loan was fully underwritten by: Bank of America Merrill Lynch, the Bank of Tokyo-Mitsubishi UFJ, Barclays Bank, Deutsche Bank, Intesa Sanpaolo, Mizuho Bank, Standard Chartered Bank, Sumitomo Mitsui Banking Corporation, and United Overseas Bank.

HSBC, which was one of the mandated lead arrangers in the 2015 loan, was not among the underwriters this time. It has also turned down a leading role in Qatar's new dollar bond, sources familiar with the decision told Reuters.

International banks are treading cautiously in order to maintain relations with both sides following June's diplomatic rift, when Saudi Arabia, the United Arab Emirates, Bahrain and Egypt cut diplomatic and transport ties with Qatar. They accused it of backing terrorism, something Doha denies.

Regional power Saudi Arabia is opening up to foreign investors as part of ambitious economic reforms driven by its new crown prince, Mohammed bin Salman, including the sale of a stake in oil giant Aramco. Its IPO could be worth $100 billion.

QNB has recently used various types of debt instruments, including Kangaroo and Formosa bonds, to refill its coffers in an effort to diversify funding resources amid the embargo imposed on Qatar by other Arab states.

The bank also recently priced a private note of $1 bln, which sources told Reuters this week that Bank of America Merrill Lynch. In addition, is raised $1.38 billion through a privately placed bond, a QNB spokesperson said on Tuesday.

(Editing by Susan Fenton) ((Tom.Arnold@thomsonreuters.com; +97144536265; Reuters Messaging: tom.arnold.thomsonreuters.com@reuters.net))