Any nuclear accord must constrain Iran's nuclear infrastructure for "decades" before the U.S. Congress will lift sanctions, 80 percent of the House of Representatives told President Barack Obama on Monday.

The 367 representatives, Democrats and Republicans, highlighted "grave and urgent" issues in the negotiations between Iran and the P5+1 group of world powers.

U.S. President Barack Obama on Monday called on Nigerians to reject violence in this weekend's general election, describing the vote as a "historic opportunity" for progress in Africa's most populous country.

"I call on all Nigerians to peacefully express your views and to reject the voices of those who call for violence," Obama said in a video message addressed "to the Nigerian people."

President Barack Obama will host Iraq's Prime Minister Haider al-Abadi next month, the White House announced on Monday.

Officials said the meeting would take place on April 14.

Israel's elections, which saw Benjamin Netanyahu clinch a third term, will not greatly affect Barack Obama's defense of any deal reached with Iran, the U.S. president said.

"I don't think it will have a significant impact," Obama told The Huffington Post in an interview Friday published in full on Saturday.

U.S. President Barack Obama on Friday urged Tehran to return four U.S. citizens captive or missing in Iran, in the latest direct appeal to the country's leaders and citizens.

Obama called on Iran to "immediately release Saeed Abedini, Amir Hekmati and Jason Rezaian" and to "work cooperatively" to find Robert Levinson "so that they all can be safely reunited with their families as soon as possible."

Marathon talks towards an Iran nuclear deal looked likely Friday to go down to the wire of a March 31 deadline, with negotiations in Switzerland set to break up and resume next week.

U.S. Secretary of State John Kerry was set to leave Lausanne Saturday after almost a week of negotiations which "resume next week", State Department spokeswoman Marie Harf said.

U.S. President Barack Obama on Thursday called his Tunisian counterpart Beji Caid Essebsi to offer condolences for the deadly museum attack and continued assistance in the investigation.

Obama "extended sympathy, on behalf of all Americans, to the victims' families and loved ones," the White House said, following the attack on the Bardo Museum in Tunis which killed 21 people.

U.S. prosecutors said Wednesday they will not pursue criminal charges against an intelligence agency employee who lost control of a hobby drone that crashed into the White House gardens, sparking a Secret Service investigation.

The man, whose name was not released, had been flying a friend's DJI Phantom "quadcopter" around his downtown Washington apartment late on January 25 and early the next morning. 

U.S. President Barack Obama and German Chancellor Angela Merkel spoke by telephone Wednesday on Ukraine, stressing they would keep up sanctions on Russia over its role in the crisis.

"There will be no easing of sanctions imposed on Russia until it has fulfilled all of its Minsk commitments," the White House said, referring to a recent deal to defuse tensions in eastern Ukraine.

Barack Obama will make his first presidential visit to Jamaica in April, a trip expected to focus on strengthening security in the Caribbean.

The White House said Wednesday that Obama would visit the island nation to meet leaders of the Caribbean bloc CARICOM.