A "Friends of Yemen" meeting, which began Thursday in London, follows announcements from the Yemeni government of Abdu Rabbo Mansour Hadi for a national conference that would pave the way to a new constitution and 2014 elections.
Hague said Hadi's "mandate for change" needed to be solidified through inclusive talks in Yemen.
"We all have no doubt that there will be differences of opinion but all should be tolerant of each other's views and see this as the place to address conflict and its underlying causes," he said.
He warned the international community wouldn't tolerate efforts, especially from outside the country, to undermine Yemen's transition.
In early February, the U.S. State Department said weapons allegedly sent by Iran to anti-government forces in Yemen are "clearly" meant as a threat to Yemen and the region.
"We must all redouble our efforts to assist them in enacting the reforms that are necessary to improve the lives of Yemeni citizens," Hague said. "The people need positive results and not empty promises."