Twitter Inc named co-founder and interim Chief Executive Jack Dorsey as its permanent CEO, ending months of speculation about who would take the reins at the company.

Dorsey will remain head of fast-growing mobile payments company Square, which he also co-founded, potentially setting up conflicts of interest.

Twitter had previously said the CEO job would be a full-time position, which seemed to exclude Dorsey if he continued to run Square.

Dorsey has served as interim CEO of the microblogging service since former CEO Dick Costolo stepped down on July 1.

Dorsey will continue to serve as a member of Twitter's board, but will no longer be chairman. Costolo resigned from the board on Sept. 30, the company said on Monday.

Some investors have expressed concerns about whether Dorsey could run both Twitter and Square, which is expected to go public later this year.

Twitter said there were no plans to provide Dorsey with direct compensation for his role as CEO.

Twitter's shares were up 3 percent at $27.10 in premarket trading.