She is the first African woman to take the award and never before has an environmental cause been honoured by the Nobel Committee since the prize was first awarded in 1901.

Maathai, Kenya's assistant minister for the environment since 2003, is the founder of the Green Belt Movement, the largest tree planting project in Africa, which aims to promote biodiversity, job creation and to give women a stronger identity in society.

The decision reflects environmentalism's extraordinary rise from the wings to the centre stage of politics, and was hailed by ecologists the world over.

Environmental movement Greenpeace welcomed the official recognition of the link between ecology and peace.

"We're clearly delighted that the influential Nobel Committee has put the green into peace," the pressure group's spokesman Michael Townsley told AFP.

Jennifer Morgan, the World Wildlife Fund's climate change director, said the Nobel decision was a "breakthrough" for recognizing that environment issues are "interwoven with security, peace, prosperity and stability".

Maathai, 64, stands at the "front of the fight to promote ecologically viable social, economic and cultural development in Kenya and in Africa," the Nobel Committee said in its citation.

"She thinks globally and acts locally," the committee said.

In Germany, Chancellor Helmut Schroeder said Maathai "had given hope to people around the world."

In Warsaw, Lech Walesa, winner of the 1983 Nobel peace price, welcomed the award of this year's prize to Maathai as "a good idea" in the face of the environmental problems around the world.

South African President Thabo Mbeki said: "Africans all walk tall today as we congratulate this remarkable woman."

Maathai said she was delighted at having won the prize and pledged to pursue her environmental work.

"I thank God and my ancestors for this award. This is a great honour for me and my fellow environmentalists who have suffered together over the years," she said at the foot of Mount Kenya.

Voted Time Magazine's "Hero of the Planet" in 1998 and a household name in her country, Maathai said the award had been the "biggest surprise in my entire life".

Deforestation has been a major problem in Kenya, exposing millions of people to drought and poverty.

Maathai's ecological campaign began in 1977 when she sowed nine tree seeds in her yard and founded an organisation which has since planted more than 30 million trees throughout Africa. The organisation and its nurseries now employ tens of thousands of people in Kenya and elsewhere.

Yet forests still cover less than two percent of Kenya's land, far below the United Nations' recommended minimum of 10 percent.

"Many wars in the world are actually fought over natural resources," Maathai told Norwegian radio. "We plant the seeds of peace, now and in the future."

Maathai is a biologist by training. She was the first woman in eastern Africa to receive a doctorate and become a professor.

The latest Nobel laureate is also an human rights activist in Kenya, and her opposition to the one-party rule of former president Daniel arap Moi led to her being jailed, harassed and vilified.

"She has served as inspiration for many in the fight for democratic rights and has especially encouraged women to better their situation," the Nobel Committee said.

Maathai was elected to the Kenyan parliament on the Green Party ticket in December 2002 in the first free elections held in the country in decades.

The choice of Maathai, which came a day after Austrian writer Elfriede Jelinek won the Literature Prize, put women centre stage in the 2004 Nobel prize season.

But experts cautioned that there was little chance that the male-dominated Nobel pantheon would become a temple of egalitarianism -- women have received fewer than one in 20 of all Nobel prizes awarded since 1901.

Choosing ecology was also seen as a decision by the five-person Norwegian committee to ease up on George W. Bush.

The last three peace laureates -- UN Secretary General Kofi Annan, former US president Jimmy Carter and Iranian human rights lawyer Shirin Ebadi -- have all been critical of the US president, who hopes to win another term in office in elections on November 2.

"These past few years, the Nobel prize has provoked criticism against the US administration. It seems reasonable to take a break from this criticism," said Stein Toennesson, head of the International Peace Research Institute in Oslo.

Maathai will receive the Nobel Peace Prize, which consists of a gold medal, a diploma and cheque worth 1.3 million dollars (1.1 million euros), at a ceremony in the Norwegian capital on December 10, the anniversary of the death of the prize's creator, Swedish inventor Alfred Nobel, in 1896.

The 2004 Nobel prize season closes on Monday with the Economics prize.

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