The move, which is due to be finalised at a meeting of EU foreign ministers in Brussels, will add new government members and relatives of Mugabe allies to an existing list of around 170 individuals banned from travelling in the bloc.
The official said some of the companies to be added to the list would for the first time be entities based in the European Union, without giving further details.
The bloc’s foreign ministers, who meet in Brussels on Jan. 26, will also add names to a list of Zimbabwean officials banned from travelling in the EU because of their links to alleged human rights abuses, a draft EU paper obtained by Reuters showed.
"The (EU) Council supports action to investigate the exploitation of diamonds from the site of Marange/Chiadzwa and their significance in possible financial support to the regime and recent human rights abuses," the document, which will be presented to EU ministers, said.
The draft urges the Kimberley Process — an international certification scheme set up to ensure diamonds do not fund conflict — "to take action with a view to ensure Zimbabwe’s compliance with its Kimberley obligations".
Alongside platinum and gold, diamonds are among the natural wealth that Zimbabwe could expect to profit from if it emerges from a humanitarian and economic crisis that has seen thousands die of cholera and inflation rocket to stratospheric rates.
The World Diamond Council industry body has put Zimbabwe’s production of rough diamonds at 0.4 percent of world production, mostly exported with the Kimberley Process certificate. However in December it raised concern about possible illegal exports "for the personal gain of a few".
Despite growing international pressure on him to step down, power-sharing talks between Mugabe and opposition leader Morgan Tsvangirai remain deadlocked in a dispute over cabinet posts.
"The (EU) Council condemns the regime for its ongoing failure to address the most basic economic and social needs of its people … The Council urges stakeholders to comply with the power sharing agreement," the EU draft said.
Critics say Mugabe’s policies, such as the seizure of white-owned farms, have ruined Zimbabwe’s economy, but the ruler — in power since independence from Britain in 1980 — blames Western sanctions for the crisis.
The EU only last December added 11 names to a list of some 160 officials, including Mugabe himself, banned from entering the bloc. The EU draft did not say how many more would be added.