Exchange operators NYSE Euronext and Deutsche Boerse AG offered more divestments in a bid to assuage European authorities' antitrust concerns over their proposed $9 billion merger.

Deutsche Boerse said in a statement on Tuesday the two companies had proposed selling more European single-equity derivatives assets than previously planned, and to offer rivals more extensive access to their clearing house for trading in innovative equity index and interest rate derivatives.

A person familiar with the matter told Reuters the companies were prepared to sell NYSE Euronext unit Liffe's single-stock equity derivatives business in Europe. A spokesman for Deutsche Boerse declined to say in which countries assets may be sold.

Deutsche Boerse's takeover of NYSE Euronext, first announced amid a rush of industry merger plans in February, would create the world's largest exchange operator.

But the European Commission has concerns that new combined entity would have too tight a grip on exchange-based derivatives trading in Europe.

In November, Deutsche Boerse and NYSE had already proposed selling overlapping parts of their single-stock equity derivatives businesses in key markets, and to open up Deutsche Boerse's Eurex derivatives clearing house to outsiders for certain products.

The companies also said on Tuesday they would license the Eurex trading system to a third party interested in launching interest rate derivatives.

FACING SCRUTINY

The European Commission is set to complete its review by February 9. The companies said they expected the deal to close after that, in early 2012.

People familiar with Deutsche Boerse's thinking told Reuters last week that the two aspiring merger partners could spin off parts of their derivatives arms to create a third-party competitor as a way to allay antitrust concerns.

EU regulators met the exchanges on Tuesday last week to discuss antitrust issues.

The project is also facing close scrutiny from German authorities. A regional regulator in the state of Hessen on Monday said it had raised some objections to the exchange operators and was awaiting a reply.

This year, Eurex and Liffe have accounted for 97 percent of European stock futures trading and 93.7 percent of stock options trading, Federation of European Securities Exchanges data shows.

The exchanges have argued their market share is much lower if the vast over-the-counter (OTC) market is included in the assessment of the derivatives market.

But their merger plans were dealt a blow when the European Union decided to exclude OTC derivatives from its review of the deal.

(Editing by Maria Sheahan and David Holmes)

Corrects to show in third paragraph source was referring only to Liffe's single-stock equity derivatives business, not its entire equity derivatives business. Also removes reference to the assets being based in London.

NYSE Euronext