Iran on Monday urged "honesty" at crucial talks with world powers due to be held this week in order to defuse a tense international showdown over its disputed nuclear activities.

"We hope the P5+1 will come to the negotiating table with honesty, and we also will make an honest effort so that both sides reach a win-win conclusion," Foreign Minister Ali Akbar Salehi told the Iranian parliament's website.

World powers will hold a fresh round of nuclear talks with Iran in Istanbul on April 14, a spokesman for European Union foreign policy chief Catherine Ashton said Monday.

"We have agreed to launch talks in Istanbul on April 14," Michael Mann said.

A German gynecologist is being investigated for allegedly having a stash of 35,000 photographs and several videos of naked patients, a report said on Saturday.

Medical assistants alerted the authorities to the collection of photographs kept by the doctor from Schifferstadt near Frankfurt in western Germany, the report by the DPA agency said.

A statement posted Wednesday on an Islamist website used by al-Qaida threatened a strike at the "heart of Berlin" unless Germany releases a jailed female militant.

"This is a special message to the old lady of Germany (Chancellor Angela) Merkel... you should learn from what happened in France," said the unsigned statement on one of the group's main sites.

An explosion at a German chemical plant killed one person Saturday and left another injured, rescuers and industrial park administrators said.

The explosion of a tank at the Evonik Degussa plant in the western town of Marl sent black smoke billowing over the town, and residents were warned to stay indoors, with their windows and doors closed.

Germany on Friday swore in new president Joachim Gauck, who warned the government that it had a historical obligation to help Europe's weakest members as they struggle to stay afloat.

Gauck, the first head of state from the former communist east, delivered the impassioned appeal for more European "solidarity" to MPs and Chancellor Angela Merkel in the light-flooded chamber of the Reichstag parliament building.

The United States said Tuesday it was exempting European Union members and Japan from tough new sanctions on Iran, praising them for reducing dependency on oil from the Islamic republic.

Under a new law aimed at pressing Iran over its nuclear program, the United States will penalize foreign financial institutions over transactions with Iran's central bank, which handles sales of the country's key export.

Germany will sell Israel a sixth nuclear capable Dolphin-class submarine, Germany's defense minister confirmed on Tuesday after talks in Berlin with his Israeli counterpart Ehud Barak.

"An additional submarine will be delivered to Israel," Thomas de Maiziere told a joint press conference with Barak, adding that Germany would subsidize the cost although he did not say by how much.

An alleged Islamic militant held for nine months in Afghanistan whose tips helped spark a travel alert in Europe in 2010 over potential attacks went on trial Monday in Germany.

The 37-year-old Ahmed Wali Siddiqui, who has Afghan and German citizenship, stands accused of membership of two "foreign terrorist organizations", al-Qaida and the Islamic Movement of Uzbekistan (IMU).

Activist pastor Joachim Gauck became German president by an overwhelming majority Sunday, marking the first time a candidate from the former communist east will serve as head of state.

Gauck claimed 991 votes out of 1,232 from a special assembly of MPs and other dignitaries, parliamentary speaker Norbert Lammert said.