Tesla still plans to release an all-electric semi-truck and is making progress on that front, Tesla CEO Elon Musk said on Twitter over the weekend.

In a reply to Electrek's Fred Lambert, Musk said Jerome Guillen, Tesla's vice president of programs who is in charge of the Tesla semi-truck project, is making progress on the project. The Model 3, however, remains top priority for the company, Musk said.

Guillen led Daimler's semi-truck program before joining Tesla in 2012. The Mercedes-Benz parent company showed off an all-electric truck designed for urban transport in November that can drive 124 miles on a single charge.

Musk first announced the semi-truck project in his "Master Plan, Part Deux" released during July of last year.

"We believe the Tesla Semi will deliver a substantial reduction in the cost of cargo transport, while increasing safety and making it really fun to operate," Musk wrote in the plan.

Although that was the first official announcement, Tesla has been hinting for quite some time that it was interested in building a semi-truck.

Tesla CTO JB Straubel discussed the role Tesla could play in the truck industry at the International Transport Forum in Germany in May 2016.

"I can’t say too much about the new products and the things we are developing, but from a pure technology point of view, everything that we’ve done on vehicles translates directly into trucks," Straubel said at the time. "There’s no reason that today you can’t make a very compelling electric truck."

Tesla is also planning to build an all-electric bus.