--EU hopes to help bridge any differences

--EU source says Commission wanted to send clear signal

--EU-Mercosur accord doesn't cover investment protection

(Adds further context, quote and details)

By Matina Stevis and Laurence Norman

Dow Jones NEWSWIRES

BRUSSELS -(Dow Jones)- The European Union has formally lodged its concerns with Argentina over speculation that Argentina may nationalize the oil company YPF SA (YPF), whose majority owner is Spain's Repsol YPF SA (REP.MC), a spokesman said Friday.

"The European Commission, through the EU delegation in Argentina, has expressed concerns to the Argentinian government," Olivier Bailly told reporters.

Bailly also said the commission, the EU's executive, was "closely watching" developments in the case and urged Argentina to "uphold its international commitments."

Bailly refused to speculate on any measures the EU could take if Argentina went ahead with the nationalization.

He noted however that investment issues aren't covered by the existing trade agreements between the EU and Mercosur, the South American trade group which includes Argentina, Brazil, Uruguay and Paraguay.

Bailly said the EU hoped to help Argentina and Spain bridge differences.

"We are here to help Argentina and Spain to find a solution to ensure a good relationship and business environment that remains conducive and agreeable to both parties," Bailly said. "We are here to...explain to the Argentine authorities that we have concerns and we'd like them to help and work with the Spanish authorities."

Bailly said European Commission President Jose Manuel Barroso hasn't spoken to Argentine President Cristina Kirchner and that he currently has no plans to do so.

An EU source said the commission had wanted to speak out clearly on the Repsol issue. The person said they expected to see a similarly strong line from other international partners in coming days. The Organization of American States meets this weekend in Cartagena, Colombia.

On Friday, Spain's foreign minister summoned the Argentine ambassador to discuss the issue. The Spanish government said it was studying measures to adopt in the dispute.

Under the 2009 Lisbon treaty, the European Commission is charged with representing the interests of European companies who have invested overseas.

News reports indicated Thursday evening Kirchner would announce some kind of action regarding YPF during an evening speech.

In the event, however, she spoke about chocolate and beef exports and ignored the YPF issue entirely.

-By Matina Stevis and Laurence Norman, Dow Jones Newswires; 003227411483; matina.stevis@dowjones.com

(Ilan Brat and the Madrid bureau contributed to this report)