A large-scale operation is under way in Syria to secure safe water supplies for more than 10 million people -- close to half the population, the United Nations Children's Fund (UNICEF) said on Monday.

The UNICEF announcement came amid reports that the quality and quantity of water is continuing to deteriorate with negative impacts for children's health.

"This shipment is very timely as supplies of chlorine in Syria have fallen dangerously low, making access to safe water challenging for many families," said Youssouf Abdel-Jelil, the UNICEF representative in Syria.

"This puts the population -- and children especially -- at high risk of contracting diarrhea and other water-borne diseases," he said.

The first four trucks carrying 80 tons of sodium hypochlorite water chlorination supplies crossed the Jordanian border into Syria on Sunday, heading for Aleppo, Hama, Idleb and Homs.

About 420,000 people -- half of them children -- need urgent humanitarian aid in Homs, UNICEF said last week, following a recent inter-agency mission to the Middle East country, which suffered from a political crisis and subsequent violence since March 2011.

Over the coming weeks, UNICEF, in coordination with the technical department of the Syrian Ministry of Water Resources and the Syrian Aran Red Crescent, will deliver 1,000 tons of chlorine to cities and communities across all 14 governorates in Syria.

Meanwhile, the World Health Organization (WHO) has co-signed an agreement with Saudi Arabia to provide 2.1 million U.S. dollars worth of essential medicines, vaccines and medical equipment. As many as 3 million Syrians will benefit from the donation, which will cover a one-year period starting this month.

A shortage of medicines in Syria is becoming more critical, as is waste management and the availability of safe drinking water, WHO has said. Poor hygiene is increasing the risk of infectious diseases such as lice, hepatitis A and leishmaniasis, a sore- causing disease transmitted by sandflies.

UN said that more than 60,000 people, mostly civilians, have been reportedly killed since the political crisis broke out in Syria some 23 months ago. Recent months have witnessed an escalation in the conflict, which has also left more than 4 million people in need of humanitarian assistance, the United Nations said.

The international community has committed more than 1.5 billion U.S. dollars for humanitarian aid to Syrians. Supporting reconstruction of critical infrastructure, such as water pumping stations, and providing essential relief supplies like medicines are among the top four priorities inside the country, along with helping people who have fled their homes and the communities hosting them and helping the poorest avoid total destitution. Endi