United Bankshares Inc. is in talks to acquire rival Washington-area lender Cardinal Financial Corp., according to people familiar with the matter, as regional banks seek to pair up to counter low interest rates and mounting regulatory costs.

United could announce a deal to buy Cardinal, which has total assets of $4.2 billion, as soon as this week, said the people, who asked not to be identified because the matter isn't public. The transaction hasn't been finalized and could still fall through, they said.

Cardinal's shares rose as much 5.4 percent and traded at $26.91 at 9:34 a.m. in New York, giving the Tysons Corner, Virginia-based company a market value of about $876 million. United Bankshares were little changed at $38.90, valuing it at about $3 billion.

Representatives for Cardinal and United Bankshares didn't respond to calls for comment outside of regular business hours.

Regional bank mergers are accelerating as lenders look to sell or bulk up to counter challenges as a result of the 2008 financial crisis. Low rates have squeezed the profitability of the industry's business model: collecting more interest from borrowers than they pay for deposits. A slew of new regulations have also hobbled key sources of non-lending income, including the fees they can charge to businesses for processing card transactions.

Florida's EverBank Financial Corp. agreed to be acquired by TIAA for close to $2.5 billion earlier this month, while FNB Corp. said in July it will pay $1.4 billion to buy North Carolina community bank Yadkin Financial Corp.

Cardinal has nearly 50 bank branches and mortgage offices in Virginia, Maryland and Washington, according to its website.

United Bankshares, based in both Washington and Charleston, West Virginia, has been eager to expand in that market, closing a purchase in June of Bank of Georgetown, a small Washington-based community bank. The about $14 billion-asset lender has more than 130 branches in Virginia, West Virginia, Pennsylvania, and Ohio.

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