“The goal is to provide details of the BHP shareholder value unlock plan to all of BHP’s shareholders so that BHP can engage openly with all parties on the plan,” Elliott said in a statement.

BHP did not immediately provide comment on the matter when contacted by Reuters.

Elliott said it holds a “long economic interest” of about 4.1% of the issued shares in London-listed BHP Billiton PLC.

That stake is worth $3.81 billion, Reuters calculations showed based on Friday’s closing price.

Elliott also said it holds rights with its affiliates to acquire up to 0.4% of the issued shares in Sydney-listed BHP Billiton Ltd, worth about $372 million.

Its letter, dated April 10 and released by Elliott online, did not mention any BHP directors by name.

Started in 1977, Elliott manages assets worth more than $32.7 billion, according to the company.

Its investors include pension plans, sovereign wealth funds and hospitals, among others, it said.

Elliott, an activist investor, also has a 3.25% stake in Akzo Nobel NV (AKZOY). It is encouraging the Dutch paints and chemicals group to enter talks with spurned U.S. suitor PPG Industries (PPG).

Elliott said its plan could increase shareholder value by up to 48.6% for holders of BHP’s Sydney shares and 51% for London shareholders.

It also proposed spinning off BHP’s U.S. oil and petroleum arm into a separate listing on the New York Stock Exchange.

It estimated the value of BHP’s U.S. petroleum business at around $22 billion.

BHP’s Australian shares closed 4.64% higher at A$25.73, with most of the gains coming near the end of trade.

BHP Billiton was created in 2001 through the merger of the Australian Broken Hill Proprietary and the Anglo–Dutch Billiton PLC.

The Australia-registered arm is one of the largest companies in Australia measured by market value. The Britain-registered arm has a primary listing on the London Stock Exchange and is part of the benchmark FTSE 100 Index.