U.N. Secretary-General Ban Ki-moon has asked his special envoy to Yemen to postpone Geneva peace talks planned for May 28, though he hopes to convene negotiations aimed at ending the war as soon as possible, the United Nations said on Tuesday.

"The secretary-general is disappointed that it has not been possible to commence such an important initiative at the soonest possible date and reiterates his call for all parties to engage in United Nations-facilitated consultations in good faith and without preconditions," U.N. spokesman Stephane Dujarric said.

Dujarric said the U.N. decision to postpone the talks was in response to a request from the government of Yemen and other parties to the conflict to have "more time to prepare."

Dujarric said Ban has instructed his Yemen envoy, Ismail Ould Cheikh Ahmed, "to redouble his efforts to consult with the Yemen government, Yemen's political groupings and countries in the region with the aim of producing a comprehensive ceasefire and the resumption of peaceful dialogue."

"Ban is acutely aware that a postponement or delay in a return to the political process will exacerbate a steadily deepening humanitarian crisis," Dujarric said.