US and EU trade officials returned to the US capital, where the talks began in July, to hammer out the Transatlantic Trade and Investment Partnership, an ambitious agreement to expand trade, investment and regulatory cooperation.
Announced by President Barack Obama and EU leaders last February, the drive is to expand the transatlantic economic relationship, already the world's largest, accounting for nearly half of global economic output.
Both sides see opportunities, beyond their already low tariffs on average, to reduce non-tariff trade barriers in a bid to stimulate new businesses and job growth.
After last month's second round of TTIP talks in Brussels, officials reported progress in discussions on services and investment.
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The new five-day round should set the ground for a political stock-taking by EU Trade Commissioner Karel De Gucht and US Trade Representative Michael Froman in early 2014, the EU said.
At stake are a range of issues, from food and aviation safety, to electric car standards and energy.
The EU wants "a better framework for regulators to cooperate," said an EU official who spoke recently on condition of anonymity. "It is important that standards (be established)... In as coordinated fashion as possible" but the United States was "not yet persuaded about that."
The US continues to argue that this issue should be addressed outside the trade deal, the official said.