U.S. Secretary of State John Kerry says "some important gaps" remain in nuclear talks with Iran, as the negotiations in Geneva prepare to go into a third day.
Kerry told journalists after talks ended Friday that the parties are "working hard."
Diplomats say the talks among Kerry, his Iranian counterpart Mohammad Javad Zarif, and key European officials made progress but say there is still work to do.
Zarif had previously indicated a preliminary agreement could be reached by Friday evening.
Russian Foreign Minister Sergei Lavrov will join the talks Saturday and China will send its deputy minister in an effort to secure a deal over Iran's disputed nuclear program.
Also Friday, U.S. President Barack Obama called Israeli Prime Minister Benjamin Netanyahu, who has opposed a potential nuclear deal with Iran. The White House says President Obama updated Mr. Netanyahu on the talks and reaffirmed his commitment to preventing Iran for obtaining a nuclear weapon.
Earlier Friday, Mr. Netanyahu met with Secretary Kerry in Tel Aviv. He told reporters ahead of his meeting with Kerry that Iran "got everything and paid nothing" because it is not reducing its nuclear enrichment capability.
"Iran got the deal of the century and the international community got a bad deal. This is a very bad deal and Israel utterly rejects it."
Major world powers are concerned that Iran is trying to develop nuclear weapons. Iran says its nuclear program is for peaceful purposes.
Speaking Friday, Kerry said diplomats are working to see if they can "narrow some differences" with Iran over the issue.
"I don't think anybody should mistake that there are some important gaps that have to be closed."
Progress was reported this week in efforts to convince Iran to scale back its nuclear program in exchange for sanctions relief.
In Washington, President Barack Obama said the deal being discussed would offer "modest relief" from the sanctions, but that most would stay in place.
It is unclear what Iran is willing to concede. Foreign Minister Zarif said Tehran is not willing to suspend its uranium enrichment program entirely, but would consider scaling it back.
This is the second meeting of the so-called P5+1 countries since Iranian President Hasan Rouhani took power in August, on promises of reaching a nuclear deal with the West.