Supporters of a U.S.-European free-trade deal have begun damping expectations about its immediate benefits amid a series of emerging disputes that could complicate the creation of the world's largest trade zone.

President Barack Obama and British Prime Minister David Cameron met Monday and affirmed that the Transatlantic Trade and Investment Partnership (TTIP) remains a top economic priority on both sides of the Atlantic — critical in Europe's quest for economic recovery.

But in recent weeks, fresh disagreements have surfaced over issues such as the regulation of financial services and the openness of U.S. state governments to foreign businesses and contractors. Those add to a healthy list of legacy disputes involving agriculture, European prohibitions on genetically modified food and French insistence that it be allowed to maintain quotas on non-French media.