DUBAI/ABU DHABI - United Arab Emirates-based Tabarak Investment has been granted more time to secure the financing it needs to buy Qatar's Commercial Bank's  40 percent stake in Abu Dhabi-listed United Arab Bank UAB.AD , sources said on Monday.

An exclusivity agreement granted to the private equity firm to finalise the purchase expired on Monday, the sources told Reuters. 

Based on UAB's current market capitalisation, the 40 percent stake held by Commercial Bank - Qatar's third largest bank by assets - is worth around 1 billion dirham ($270 million).

One source said the delay was due to a cross-border bank guarantee Tabarak needed from an international lender to secure some of the financing for the deal.

Qatar has been embroiled in a diplomatic and commercial row with UAE, Saudi Arabia, Bahrain and Egypt since June 2017.

Since it began talks in September with Commercial Bank about the purchase, Tabarak has required several extensions of the exclusivity period.

A second source said no further formal extension had yet been agreed.

UAB did not respond to a request for comment. Commercial Bank and Tabarak declined to comment.

Tabarak has a stake in Dubai's Drake & Scull International  and investments in education, industry, logistics and healthcare.

($1 = 3.6724 UAE dirham)

(editing by John Stonestreet) ((Tom.Arnold@thomsonreuters.com; +97144536265; Reuters Messaging: tom.arnold.thomsonreuters.com@reuters.net))