Speaking on June 13, Obama said he'll review those options in the coming days.
But he said any U.S. action would need to be accompanied by efforts from Iraqi leaders.
"We can't do it for them," Obama said.
He added that the threat by militants from the Islamic State in Iraq and the Levant (ISIL) poses a danger to the people of Iraq and also, potentially, to U.S. interests.
Obama said the Iraqi government must make a sincere effort to address sectarian Sunni-Shi'a differences, or else U.S. military help won't succeed in curbing the insurgency there.
Obama spoke just before departing Washington en route to North Dakota.
ISIL insurgents this week captured two provincial capitals -- Mosul, Iraq's second-largest city, and Tikrit -- in a rapid southward advance through Sunni-majority parts of Iraq.
In their latest push, the insurgents captured two more towns -- Saadiya and Jalawla in Diyala Province -- late on June 12.
The advance prompted Iraq's most senior Shi'ite cleric to issue a call to take up arms to defend the country.
The call by a representative of Grand Ayatollah Ali al-Sistani came during Friday Prayers on June 13.
In his sermon in Karbala, Sheik Abdulmehdi al-Karbalai said: "He who sacrifices for the cause of defending his country and his family and his honor will be a martyr."
The Reuters news agency reported that Sunni insurgents fought Shi'ite militia at two locations in Diyala Province on June 13 -- in Udhaim and in Muqdadiya, located less than 100 kilometers from Baghdad.
As militants move south, vowing to take Baghdad and regions dominated by Iraq's Shi'ite majority, an Interior Ministry spokesman said the capital's defenses had been bolstered in preparation.
Prime Minister Nuri al-Maliki said the government would arm and equip citizens who volunteer to fight.
Speaking on a visit to London on June 13, U.S. Secretary of State John Kerry urged Iraq's political factions to unite, saying, "Now's the time for Iraq's leaders to come together and to show unity."
He also said he expects Obama to make "timely decisions" on Iraq due to the gravity of the situation.
Iranian President Hassan Rohani called Maliki on June 12 and promised that Iran "will apply all its efforts on the international and regional levels to confront terrorism."
UN Calls For 'Inclusive Dialogue'
Earlier, the UN Security Council called on June 12 for an urgent dialogue in Iraq and condemned "terrorist" activities, but stopped short of considering any action against Islamic militants.
Russia's UN ambassador, Vitaly Churkin, the council president, said the 15 members expressed unanimous support for the government and people of Iraq in their fight against terrorism and stressed the importance of an "inclusive national dialogue."
At a news conference in Baghdad, UN envoy Nickolay Mladenov said Iraq "now faces the biggest threat" to its sovereignty and integrity "for a number of years."
"It is time for the political leaders of this country to come together, to put their differences aside, and to work jointly for the future of Iraq," Mladenov added.
Meanwhile, U.S. weapons maker Lockheed Martin said on June 12 it was evacuating about two dozen employees from northern Iraq. The U.S. State Department said other companies were relocating workers as well.
The UN's high commissioner for human rights, Navi Pillay, on June 13 expressed "extreme alarm" at the deterioration of the situation in Iraq, amid reports of summary executions and extrajudicial killings and the displacement of 500,000 people.
UN human rights spokesman Rupert Colville later said hundreds of people were killed, many of them summarily executed, after ISIL militants overran Mosul this week.
Colville told a news conference in Geneva that people had been stopped at government checkpoints and prevented from fleeing Mosul as Sunni Islamists entered the city.
"We've received reports of the summary execution of Iraqi army soldiers during the capture of Mosul and of 17 civilians in one particular street in Mosul city on June 11," he said.
Elsehwere, the International Organization for Migration said on June 13 that 40,000 people were estimated to have fled from Tikrit and Samara in addition to the 500,000 who are thought to have left Mosul.
Oil Prices Rise
In related news, crude oil prices have risen to 10-month highs amid concerns that developments in Iraq may affect global oil supplies.
The benchmark U.S. oil contract for July delivery rose above $107 a barrel in electronic trading on the New York Mercantile Exchange early on June 13.
On June 12, the contract jumped $2.13.
The rise comes as Iraq's widening insurgency is fueling fears over supplies from the second-biggest producer in the OPEC oil cartel after Saudi Arabia.