Hague said while the situation was of great concern, the government was "not countenancing at this stage any British military involvement"
He said he believed Iraq had sufficient forces to counter the threat.
A US official said the United States "stands ready" to help Iraq, but made no mention of sending troops.
Having overrun Iraq's second city of Mosul in a spectacular assault this week, militants from the Islamic State of Iraq and the Levant (ISIL) seized the city of Tikrit today.
Also Read
Hague urged Iraq's political leaders to find a rapid solution to the deadlock over forming a new coalition government, and said the insurgency proved the war in Syria was "infecting" the region.
British troops were the second largest force behind the United States in the 2003 invasion of Iraq.
But Hague dismissed suggestions that the invasion to topple Saddam Hussein had left Iraq vulnerable to such insurgencies.
"We are very worried about this," he told ITV News.
"It's very important that the civilian population are protected as well as possible, that people who are fleeing the area are looked after by the Iraqi authorities and people in neighbouring countries as well.
"And it shows how important it is for the Iraqi leaders to form a new government quickly.
"They've just had an election.
"And to have the political unity and consensus to deal with this."
Asked if Britain would offer military assistance to Baghdad, he said: "It's for Iraq primarily to respond to this.
"Iraq has considerable resources.
"It has its armed forces.
"We're not countenancing at this stage any British military involvement."