"Iran right now is enriching the uranium ... [but] the question of manufacturing a [nuclear] weapon is a different thing ... . Whatever time is left, there is not a lot of time." Netanyahu said.
At a news conference in Jerusalem, Obama appeared to agree, with the proviso that Israel work with the United States to prevent an Iranian nuclear capability.
"I'm absolute convinced the president is committed to preventing Iran from getting nuclear weapons," Netanyahu said.
Asked by a reporter whether Syria has crossed a U.S. "red line" by using chemical weapons against insurgents in that country's civil war, Obama said, "We have been clear that the use of chemical weapons against the Syrian people would be a serious and tragic mistake," adding that those who use them will be "held accountable for the use of chemical weapons or their transfer to terrorists."
Syrian rebels claimed the Bashar Assad regime fired Scud missiles with chemical warheads at insurgents earlier in the week. The regime responded that it was the rebels who used such weapons.
Obama indicated the United States did not know yet what had occurred.
"With respect to chemical weapons we intend to investigate thoroughly exactly what happened ... to find out precisely whether this 'red line' was crossed," the president said. "Once we establish the facts, I have made clear that the use of chemical weapons is a game-changer."
Obama said any response must be international, not unilateral on the part of the United States.
The president said he and the prime minister discussed the use of a two-state solution in the peace process. "A central element of a lasting peace must be a strong and secure Jewish state ... alongside a strong and independent Palestinian state," Obama said.
He also pledged to see that U.S. military aid to Israel continued beyond the end of current commitments in 2017, and said Egypt must remain a player in regional security.
Earlier, Obama and Netanyahu, despite a sometimes testy relationship, joked like old friends as they met.
The jokes before the two leaders sat down to dinner added color to a trip that so far has had more symbolic gestures than substance.
Obama and Netanyahu met just outside the prime minister's residence.
When they paused for a photo-op with Netanyahu's wife Sara between them, Obama said she was a "rose between two thorns."
"You obviously knew exactly when to come," Netanyahu said, referring to the recent Israeli elections and formation of a Cabinet. Netanyahu said Obama was lucky, "you only have one party." Multiple parties in Israel formed a coalition for the new government.
Obama, who has his own political problems at home, replied, "The grass is always greener, my friend."
They then entered the formal dining area in Netanyahu's home, which had modern art on the walls and 16 chairs around a rectangular table.
Obama, after declaring an "unbreakable bond" between the two countries, met privately earlier Wednesday with Israeli President Shimon Peres.
After the meeting, Peres said he and Obama share a common view -- that the "two-state solution," a Palestinian state alongside Israel, is the goal.
"We share a common vision; we mustn't let the skeptics win," Haaretz quoted Peres as saying. "We agree that the goal is a two-state solution. We consider Abu Mazen [Mahmoud Abbas, Palestinian Authority president] as our partner in the effort to stop terror and bring peace. Hamas remains a terror organization that targets innocent people. In the north, Hezbollah targets innocent people across the world. Hezbollah is destroying Lebanon and sponsoring massacres in Syria. We cannot allow chemical weapons to fall in terrorists' hands. There is an attempt to bring spring; it is an Arab initiative, which might bring peace. If realized, it will bring a better tomorrow. There is a division between skeptics and those who bring peace. Your voice is of optimism."
Obama thanked Peres for a warm welcome.
" I am especially thankful for the time you allowed me to share with the Israeli boys and girls," the U.S. leader said. "They want to be safe, free from rockets; they want a world where science and technology are used for peace, for learning."
During their closed-door meeting, which included U.S. Secretary of State John Kerry, Peres was expected to thank Obama for the U.S. investment in the Iron Dome anti-missile system, tell him Israel and the United States are united in facing down Iran's development of a nuclear weapon, and demand the United States cooperate with Israeli efforts to contain Syria's chemical weapons caches, Haaretz reported from Jerusalem.
Before the meeting, Obama, shovel in hand, walked with Peres through the presidential garden to plant a magnolia tree brought from the White House as a gift.
"A magnolia tree, just like what we have outside the White House," Obama told reporters. "I want everyone to know, this was on Air Force One."
Earlier in the day, Obama said he considers his first visit to Israel as president a chance to reiterate the "unbreakable bond" between the two nations.
"I see this visit as an opportunity to reaffirm the unbreakable bond between our two nations," Obama said at Ben Gurion Airport in Tel Aviv, where he began his three-day visit to the United States' closest ally in the Middle East. "We share a common story."
Obama said peace must come in the Middle East and ended his remarks reaffirming an "eternal alliance" between the United States and Israel.
Netanyahu, noting Obama chose to travel to Israel as the first foreign trip of his second term, said, "I come here today with a simple message for you and the people of the United States: Thank you ... for standing with Israel."
Netanyahu thanked the American president for military aid, supporting Israel at the United Nations and for the "unbreakable U.S. bond."
Welcoming Obama, Peres said his visit was a "demonstration of the profound relationship between our two countries. ... Thank you for [the] way you are, thank you for what you do. Thank you for the hopes you carry with you."
Obama deplaned Air Force One to an honor guard from all branches of the Israeli military and small crowds sitting in bleachers lined with Israeli and U.S. flags and flowers.
After Obama and Peres inspected the troops, they and Netanyahu walked a receiving line of civil and religious dignitaries, and members of the new Israeli government. Following the welcoming ceremony and remarks, Obama inspected an Iron Dome battery and other air defense systems outside a hangar on the tarmac.
The White House said the Iron Dome is a short-range rocket and mortar defense system developed by Israel and produced with U.S. assistance that is part of a multi-tier missile defense structure devised as a countermeasure to the rocket threat against Israel's civilian population.
The state visit includes trips to the Yad Vashem holocaust memorial, Mount Herzl and the Israel Museum.
In Jerusalem, Obama will attend a reception at the President's Residence, followed by a meeting with Netanyahu at his residence.
Kerry arrived in Israel Tuesday. His schedule indicated he would spend time on the Israeli-Palestinian diplomatic process, the Post said.
Haaretz reported Palestinian groups were organizing a demonstration Thursday in Ramallah, West Bank, to protest Obama's visit.
"Obama is coming to strengthen Israel, which means continued occupation and settlement," one of the organizers, Hazem Abu Hilal, said.
Obama travels to Jordan Friday to meet with King Abdullah II.