The Saudi Stock Exchange suspended trading in shares of Alawwal Bank and Saudi British Bank at the companies' requests, saying the two banks "will announce an event."

The two Saudi lenders have been in merger talks since late April 2017. The potential transaction has taken longer than expected as the regulatory environment for mergers in Saudi Arabia is relatively untested, with the last significant merger taking place about 20 years ago, Reuters reported in January.

The stock exchange, also known as Tadawul, said shares in Alawwal Bank will resume trading once the bank announces its event. On the other hand, the trading suspension on Saudi British Bank's shares will be lifted May 16.

Royal Bank of Scotland Group PLC holds a 40% stake in Alawwal Bank, while HSBC Holdings PLC owns a 40% stake in Saudi British Bank, according to S&P Global Market Intelligence data.