A logo of the Swiss mining company Xstrata is pictured at its headquaters in Zug Reuters

Glencore International has increased its takeover bid for global mining group Xstrata, the company said, only minutes before its shareholders we due to vote on a controversial $80bn merger with the commodities dealer.

Xstrata told shareholders who were meeting in Zug, Switzerland, that it had received a last-minute proposal from Glencore that would increase the terms of its proposed bid - taking the value to $37bn - and make Glencore CEO Ivan Glasenberg the new boss of the merged company, a position previously set up for Xstrata CEO Mick Davis.

Glencore's new bid, Xstrata says, is worth 3.05 Glencore shares. Qatar Holdings, which is controlled by the country's royal family, has said previously it would like to see the bid improved to 3.25 Glencore shares.

"This is not a firm offer," Xstrata said in a statement. "Any elements of the proposal remain subject to change and the proposal also remains subject to Xstrata board approval."

A new meeting will be scheduled to decide on the terms, Xstrata said. Under its own company laws, a new meeting can't be held for at least 30 days.

The decision comes just hours after Glencore's own shareholder meeting descended into chaos as Chairman Simon Murray was forced to adjourn it minutes before shareholders were due to vote on the bid for Xstrata. Glencore executives have been attempting for months to convince Xstrata's largest shareholders - Qatar Holding and Knight Vinke Asset Management - to accept Glencore's offer of 2.8 shares for each Xstrata share, a deal which would value the combined group at $34bn.

However, both investors, who own around 12.5 percent of Xstrata, have been pushing for a larger ratio of Glencore shares in order to accept a merger or a takeover, according to several media reports, and have said they would vote against the deal if it wasn't improved.

Glencore needs both investors to support the deal because it can't vote its own 34 percent holding in Xstrata under the terms of the original approach it made back on 2 February. As a result, only 16.5 percent of shareholders would need to vote against any deal in order for it to be blocked.

Xstrata shares have surged in London trading following the day's developments, trading 5.5 percent higher at 1,034 pence per share. Glencore shares have fallen more than 5.1 percent to 372.3 pence.