UNITED NATIONS - UN agencies are stepping up their relief efforts to those affected by Typhoon Haiyan, which buffeted the Philippines a week ago, flattening towns and cities and claiming thousands of lives, a UN spokesman said here Monday.

"Nearly 13 million people across nine regions have been affected by Typhoon Haiyan, including more than 4 million people who have been displaced and some 2.5 million people who require food aid," said Farhan Haq, acting deputy spokesperson for UN secretary-general, at a daily briefing.

For the past 48 hours, the UN Children's Fund (UNICEF) has been trucking and airlifting water and sanitation supplies to Tacloban, a coastal city about 360 kilometers southeast of Manila, the national capital, and other affected areas to restore clean water supplies and reduce the threat of diseases caused by poor sanitation and contaminated water, he said.

At least 200,000 people in Tacloban and six surrounding districts were receiving clean water, with the first water treatment plant resuming operation last night, Haq said, citing UNICEF's reports.

"UNICEF, the Philippines armed forces and the US Agency for International Development took part in negotiations resulting in an initial emergency fuel supply to run the plant for four days," he added.

Meanwhile, UN Humanitarian chief Valerie Amos has arrived in the Philippines and is expected to visit affected areas in the coming days, the spokesman said.

Last week, the UN and its partners launched an appeal for $301 million to provide humanitarian assistance. As of Saturday, the UN has received 26 percent of the funding.

UN Secretary-General Ban Ki-moon, who left Lithuania Monday, said the recent typhoon in the Philippines is a "wake-up call" for the international community to accelerate its efforts to fight climate change.

"Therefore, it is imperative that member states redouble their efforts to raise the level of ambition and there should be a strong political leadership role," said Ban, who would head to Warsaw, capital of Poland, later Monday for the UN climate change conference there.