The US Department of Justice (DoJ) is looking for more information in its examination of the anti-trust implications of Oracle's proposed acquisition of Sun.

The DoJ is now seeking to extend the examination beyond an initial review period. The department said that it was "almost able" to resolve all the issues, but a "narrow issue" related to the way Java rights are licensed remains outstanding.

"[That issue] is never going to get in the way of the deal. I fully expect that the investigation will end soon and not delay the closing of the deal this summer," said Oracle counsel Dan Wall from Latham & Watkins.

The deadline for the DOJ's initial 30-day review period was set to expire at midnight on Friday, according to reports in The Wall Street Journal and Reuters.

Oracle agreed to acquire Sun in April for $7.4 billion (£4.5 billion), after Sun reportedly rejected a purchase offer from IBM. During a press conference to discuss the deal, Oracle CEO Larry Ellison said Java and Solaris were the two main reasons why Oracle wants to buy Sun.

Ellison called Java "the single most important software asset we have ever acquired" and added that Oracle's Java-based middleware business, bolstered first by the BEA acquisition and now by the purchase of Sun, is on track to become as large as Oracle's flagship database business.

In early May, Sun disclosed in a filing with the US Securities & Exchange Commission that Sun shareholders had filed three separate lawsuits challenging the proposed sale of the company to Oracle.

The suits, filed in Santa Clara County, California, superior court, name Sun, some of its officials and Oracle as defendants, according to the filing.

All three actions are aimed at blocking the sale, alleging the price tag is "unfair and inadequate." They also allege "claims for breach of fiduciary duty against the individual defendants and for aiding and abetting a breach of fiduciary duty against the corporate defendants," the filing states.