U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif on Wednesday concluded three days of negotiations on the Islamic Republic's nuclear program, and an unidentified senior State Department official told Reuters that both sides had inched closer to a deal.

"We have made some progress but have a lot of challenges yet ahead," said the official, who was traveling with Kerry. "The bottom line here is that (there is) no deal to announce to anybody today."

The United States and Iran would "regroup bilaterally" and negotiators would most likely meet again on March 15, possibly in Geneva, about 60 miles east of Montreux, the Swiss town where this week's discussions took place.

"There are still significant gaps and important choices that need to be made," Kerry acknowledged. Zarif, meanwhile, similarly told reporters that progress had been made. "But a lot of work remains," the Iranian top diplomat cautioned.

Wednesday's talks were somewhat overshadowed by the controversial speech Israeli Prime Minister Benjamin Netanyahu had given before the U.S. Congress the day before, Reuters noted. Netanyahu suggested that the emerging deal between the United States and Iran would "all but guarantee" that the Islamic Republic would eventually acquire nuclear weapons.

"This deal will not change Iran for the better. It will only change the Middle East for the worse," Netanyahu said, according to Fox News. "If the deal is signed, they're only a year away from the bomb," he added.

President Barack Obama on Tuesday chided Netanyahu for what he claimed was the premier's failure to offer any "viable alternatives" to the current negotiations. His secretary of State agreed on Wednesday, insisting that politics and external factors would not distract from the talks with Tehran.

"No one has presented a more viable, lasting alternative for how you actually prevent Iran from getting a nuclear weapon," Kerry argued. "So, folks, simply demanding that Iran capitulate is not a plan. And nor would any of our P5+1 partners support us in that position."

The secretary was referring to the four remaining permanent members of the U.N. Security Council -- China, France, Russia and the United Kingdom - and Germany, all of which also participated in the talks. Representatives of the European Union have been invited, as well, and will most likely be present when the negotiations resume in mid-March.