UPDATE 2-US demands UBS "comply in full" in tax evasion case

* Aims to ensure taxpayers comply on offshore accounts

* Comes despite recent media speculation about settlement

* US says has proven case for enforcement of UBS summons

* Tells court UBS "actively helped" Americans break US law

* UBS says US asking it to break Swiss law (Adds information from court document, quotes from second attorney)

By Tom Brown

MIAMI, June 30 (Reuters) - The U.S. Justice Department said on Tuesday it was pressing ahead with its five-month-old lawsuit against UBS AG to force the Swiss bank to identify thousands of U.S. clients with secret UBS accounts.

Despite recent media speculation about a possible settlement of the case, the Justice Department said in a brief filed with a Florida court that it was seeking to enforce tax compliance with the full weight of U.S. law.

"The United States has a strong national interest in making sure that all U.S. taxpayers comply with the tax laws, including disclosing their offshore accounts, and paying all the taxes they owe," the department said in the brief.

The U.S. government sued UBS (UBSN.VX)(UBS.N) in February in the U.S. Southern District Court of Florida, seeking the names of 52,000 Americans suspected of using the bank to hide nearly $15 billion in assets and evade U.S. taxes.

"The United States has proven its case for enforcement. The Court should order UBS to comply in full," the Justice Department said in its filing.

In response, a spokesman for UBS said enforcement of the U.S. summons would require the bank to violate Swiss law and was inconsistent with U.S.-Swiss treaty frameworks.

A court hearing on the U.S. government case against UBS has been scheduled for July 13.

Attorneys and analysts have been skeptical about media reports that the United States would drop the case against UBS without major Swiss concessions, given the international momentum against tax havens and the coming deadlines for errant U.S. taxpayers to come forward voluntarily.

"Based on our representation of many UBS cases, it is clear in our minds that the government is going to pursue vigorously its objectives of transparency and limiting tax haven abuse," attorney William Sharp, who represents U.S. clients of UBS, told Reuters by phone.

UBS and the Swiss government have argued that any exchange of confidential banking information should be handled through existing legal treaties rather than in the courts.