Malaysian banks are stepping up their expansion plans.

Less than a week after RHB Bank and AMMB Holdings received the regulatory go-head to start merger talks, the country's second largest lender CIMB Group (Kuala Lumpur Stock Exchange: CIMB-MY) said it sold a 50 percent stake in its stockbroking unit to China Galaxy Securities.

"We have always been strong here in Southeast Asia. But it comes to our strength outside of Southeast Asia, we find it very hard to compete but this, this is a good step," CIMB Group's chief executive Zafrul Aziz said on CNBC's "Street Signs" on Thursday, two days after signing the deal.

"The synergies are great. We are seeing opportunities with the belt and road initiative that's been announced … With this collaboration we have just formed with China Galaxy, it will facilitate the capital market, we will be there to support Chinese companies and also us Southeast Asian companies to go to China. "

The stake sale of CIMB Securities International would see CIMB Group (Kuala Lumpur Stock Exchange: CIMB-MY) and China Galaxy run a 50:50 stockbroking joint venture outside of Malaysia. The unit comprises institutional and retail brokerage, equities research and associated securities business across Indonesia , Singapore , Thailand , Hong Kong , South Korea , India , U.K . and U.S.

CIMB's latest announcement came two years after the collapse of a potential $20 billion three-way merger to form one of Southeast Asia's largest financial groups. If the plan had gone ahead, the merger of CIMB, RHB (Kuala Lumpur Stock Exchange: RHBC-MY) and Malaysia Building Society would have overtaken Maybank (Kuala Lumpur Stock Exchange: MBBM-MY) as the largest banking group in the country.

Changed market conditions were cited as reasons behind the failed plan.

In the next few months, the Malaysian banking sector could see its largest deal with the merger of RHB and AmBank to form a group worth about $9 billion.

When asked about possible mergers or acquisitions, Zafrul said he is happy with CIMB's current size.

"In any country, banks need scale. If you do not have that scale, you're not operating at your optimal performance. For CIMB, we are happy with the size and we are benefiting from the scale. If there is to be any merger with CIMB, it has to be something that's really good in terms of returns," he said.

"The problem with mergers at this scale is it involves around a lot of synergies, it involves costs so revenue synergies would be limited in that sense … and cost synergies are very hard to execute."