Prime Minister Tony Blair, Conservative leader David Cameron and Liberal Democrat leader Sir Menzies Campbell have given their backing to the new Darfur and Chad appeal launched this week by the Disasters Emergency Committee.

The three leaders appealed to the public to give generously in order to save lives in Darfur, Chad and the Central African Republic.

International aid agencies behind the appeal, including Tearfund, Christian Aid and World Vision, warned that looming rains will bring the risk of deadly conditions like diarrhoea and malaria to the estimated 4.5 million currently affected by the ongoing conflict, particularly children, pregnant mothers and older people.

The aid agencies are appealing to the public to donate now in order that the medicines and resources needed to cope with the emergency are already in place before the rains arrive and make impede access to those in need.

Mr Blair said he hoped people would be "generous" in giving to the DEC appeal, calling the crisis in the region a "very serious situation in deed".

"Many people have died but also many people are in a situation of the most dire need. So I hope and I am sure the British people will respond generously as they always do and this will be obviously in addition to the money that the UK government has been putting into the situation and in order to alleviate the humanitarian suffering," said Mr Blair.

He said that the UK was pressing the Sudanese government to stop the bombing and the violence in the region and added that he would continue working for a "very tough" United Nations Security Council resolution if Sudan ignores the appeal currently being launched by the United Nations Secretary General.

"This is a very serious situation, it needs our help and it needs your help too," he stressed.

The appeal was launched on Thursday by leading charities in the UK including World Vision, the British Red Cross, CAFOD, CARE International UK, Christian Aid, Concern Worldwide, and Tearfund.

Violence is spreading throughout the region with many villages now burnt out shells. In Darfur alone, two-thirds of the population are dependent on aid. Money raised by the appeal will help people affected by the conflict, giving shelter, clean water and sanitation, emergency food and vital items such as water buckets, blankets and soap, and will enable medical teams to provide emergency care.

Mr Cameron said that the humanitarian crisis in Darfur is "quite simply the worst in the world" and that "we must do more about this".

"The only thing standing between these people and starvation and death are the international aid agencies. The rainy seasons are coming and the conditions are going to get worst and we've got to back our aid agencies," he said. "So I would urge you to give generously to this vital appeal and to back the fantastic work that our aid agencies are doing."

He also urged the British public to keep pressure on politicians to ensure they play their part in securing a long-term solution for the conflict in the region.

Sir Campbell said that the situation for millions in Darfur was so serious that it could not wait for the UN to take more action. "They need your help now," he said.