The Shenzhen Stock Exchange has asked China Vanke's two largest shareholders to clarify whether they are acting in concert to block the company's 6.9-billion-US-dollar deal with the Shenzhen Metro Group.

Vanke's management announced the agreement with Shenzhen Metro in March that would make the state-owned subway operator its largest shareholder.

Vanke hoped the deal would counter a hostile takeover bid by financial conglomerate Baoneng by diluting the stakes of Baoneng and state-owned China Resources.

Baoneng responded late last week by calling for the ouster of Vanke's board.

China Resources has said separately that it opposes the Shenzhen Metro deal and would vote against it.