Chemical giants Dow and DuPont on Thursday won approval from US antitrust officials to merge, clearing the last major hurdle to the proposed deal.

US Justice Department antitrust officials did not require additional divestitures beyond those mandated earlier by the European Union, the companies said in a news release.

The proposed merger of two of the world's largest chemical companies, with a combined market value of nearly $150 billion, would see Dow divest a global polymer business and DuPont give up part of its crop-protection product business.

The companies reaffirmed expectations that the merger deal will close in August, after which they will split into three independent companies within the following 18 months.

"With today's DOJ clearance, we have taken a significant step forward in bringing together these two iconic enterprises," Dow's chairman and CEO Andrew Liveris said in a statement.

He said the three new companies will be "leading, independent innovation-based science companies that will generate significant benefits for all stakeholders."

The Justice Department said the planned divestitures would resolve an anti-trust lawsuit filed jointly on Thursday with three state attorneys general over concerns US farmers could be harmed by a lack of market competition for crop protection products and food packaging.

The European Commission granted approval to the merger in March contingent on the selloffs.

Originally announced in December 2015, the merger had been closely scrutinized by antitrust regulators globally.