DUBAI, Nov 22 (Reuters) - Investcorp has bought a stake in Saudi Arabia's Al Borg Medical Laboratories, one of the largest private medical laboratory chains in the Gulf, it said on Tuesday.

The alternative investment firm did not disclose the size of the stake or the amount it was investing, although a source close to the deal said Investcorp was investing in the range of $100 million to $200 million for a 30 to 40 percent stake in the company.

Investcorp, which expects to reach its target of $25 billion for assets under management (AUM) next year, has made several investments in the past 12 months, most recently the debt-management business of Britain's 3i Group PLC for 222 million pounds ($277 million).

Al Borg has 53 laboratories across eight countries in the Gulf and Africa, offering medical laboratory testing services to hospitals, clinics, companies and individuals.

The companies said the investment would help Al Borg to expand in the kingdom and further afield in the region.

"The healthcare sector in Saudi Arabia is highly defensive and underpinned by favourable demographics, supportive regulations and greater medical awareness," said Mohammed al-Shroogi, co-chief executive of Bahrain-based Investcorp.

Investcorp's last investment in Saudi Arabia was in January 2016 when it invested in Bindawood Holding, one of the leading supermarket and hypermarket chains in the kingdom.

($1 = 0.8010 pounds)

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