Citizens Bank of Massachusetts said Tuesday it has completed its purchase of $770 million-asset Grove Bank of Newton and Brookline.

The $5 billion-asset bank, a unit of Citizens Financial Group Inc., Providence, R.I., unveiled the $90.5 million acquisition Nov. 4. The transaction also included Greater Boston Bank, which Grove acquired in January.

Lawrence K. Fish, Citizens Financial Group's chairman, said in a prepared statement that the purchase meshes well with Citizens' supercommunity commercial and retail banking strategy, "and provides us with a strong foundation for future growth."

Citizens remains the Bay State's fourth largest bank in terms of assets, behind units of Fleet Financial Group, Bank of Boston Corp., and State Street Boston Corp.

Although Grove is being merged into Citizens, the conversion of systems and accounts won't be complete until around September, spokeswoman Arlene Fortunato said. Until then, Grove branches will operate under the banner, "Grove Bank, a Citizens Bank company."

With the purchase of Grove, Citizens now has 75 branches in Massachusetts. None of Grove's nine offices are being closed, but there "most likely will be consolidation" over time in one or two towns where both Citizens and Grove have a presence, Ms. Fortunato added.

Citizens Financial Group, which has $16 billion of assets, has made 10 acquisitions in New England-half of them in Massachusetts-since 1992. It is owned by Royal Bank of Scotland and Bank of Ireland.

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