US President Barack Obama has invoked former President John F. Kennedy’s words about negotiations as talks over Iran’s civilian nuclear program a self-imposed end-March deadline for reaching a mutual understanding approaches.

Speaking at the dedication of the Edward M. Kennedy Institute for the US Senate in Boston on Monday, Obama said Secretary of State John Kerry had wanted to be at the negotiations.

“As many of you know, John is in Europe with our allies and partners leading the negotiations with Iran and the world community and standing up for the principle that Ted and his brother, President Kennedy, believed in so strongly,” Obama said.

“Let us never negotiate out of fear, but let us never fear to negotiate,” Obama said, quoting a famous line from JFK's 1961 inaugural address.

US President John F. Kennedy delivers his inaugural address after taking the oath of office at Capitol Hill in Washington, DC on January 20, 1961. (AP file photo)

Top officials from Iran and the P5+1 – the US, Britain, France, China, Russia and Germany – are engaged in intense negotiations in Lausanne, Switzerland, to reach a comprehensive deal on the Islamic Republic’s nuclear program. The two sides have set July 1 as the deadline for a final agreement.

Sources close to the Iranian negotiating team say the main stumbling block to resolving the Western dispute over Iran’s nuclear issue is the timetable for the lifting of anti-Iran sanctions.

US Secretary of State John Kerry told a CNN correspondent in the Swiss town of Lausanne on Monday that he and his global counterparts were working hard to resolve "tricky issues" obstructing a nuclear agreement with Iran.

"There still remain some difficult issues. We are working very hard to work those through. We are working late into the night and obviously into tomorrow," Kerry said.

Iranian and US negotiators wait to start a meeting at the Beau Rivage Palace Hotel on March 29, 2015 in Lausanne, Switzerland. (AFP photo)

On Monday, Iranian Foreign Minister Mohammad Javad Zarif held a meeting with Kerry, German Foreign Minister Frank-Walter Steinmeier, French Foreign Minister Laurent Fabius, Chinese Foreign Minister Wang Yi, Russian Foreign Minister Sergei Lavrov, British Foreign Secretary Philip Hammond and High Representative of the European Union for Foreign Affairs and Security Policy Federica Mogherini.

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