(Adds comment from Juba)

By Tom Miles

GENEVA Oct 22 (Reuters) - South Sudan faces a serious risk of famine by the end of this year and 30,000 people are already classified as being in a food security catastrophe, the Integrated Food Security Phase Classification (IPC) said on Thursday.

Hunger in the world's newest state has grown steadily worse in the nearly two years since a political crisis led to fighting that reopened ethnic fault lines between President Salva Kiir's Dinka people and ethnic Nuer forces loyal to former Vice President Riek Machar.

The two have signed a series of peace deals but fighting rages on.

The IPC, whose members include the U.N. Food and Agriculture Organization (FAO) and the World Food Programme (WFP), said famine had not been officially declared because it was hard to get data from conflict zones.

But there is a "likelihood" of famine occurring in the coming months in parts of oil-rich Unity State, one of the hardest-hit areas, unless urgent humanitarian access is allowed.

"There is a great concern that famine may exist in the coming months but it may not be possible to validate it at that time due to lack of evidence as the result of limited access to the affected areas and populations," it said.

South Sudan's government agriculture minister Beda Machar told a news conference there was no "famine" in the country and the food security situation has in fact improved

"We advise against the irresponsible use of a word such as "famine" by stakeholders, including the media," the minister said.

Intense fighting in some parts of the country has forced humanitarian groups to pull out, and they say displaced families are surviving on just one meal a day. In extreme cases, people fleeing violence survive by eating water lilies.

This marks the first time since the conflict erupted that the ICP has identified that some in South Sudan have reached the fifth phase - catastrophic food insecurity - on its five-point scale.

"This is the start of the harvest and we should be seeing a significant improvement in the food security situation across the country," said WFP Country Director Joyce Luma.

"Unfortunately this is not the case in places like southern Unity State, where people are on the edge of a catastrophe that can be prevented," Luma said. (Additional reporting by Denis Dumo in Juba; writing by Edith Honan; Editing by Angus MacSwan)