( CNN ) UNICEF said Friday that an initial shipment of 16 tons of medical supplies , meant to help 80,000 innocents caught up in the havoc of Yemen , had at last landed in Yemen 's capital , Sanaa . The conflict is exacting a heavy toll on children and families , UNICEF said in a statement . `` The humanitarian situation is worsening all the time , with increasingly limited access to water , basic sanitation and critical health services , '' the statement quoted UNICEF Yemen representative Julien Harneis , speaking from Amman , Jordan , as saying . `` The supplies we have managed to bring in today can make the difference between life and death for children and their families -- but we know they are not enough , and we are planning more of these airlifts . '' Aid agencies have been saying that supplies were desperately needed , but getting them into the country in the midst of regional turmoil was difficult . UNICEF said its cargo included antibiotics , bandages , syringes , IV sets and other medical supplies . Included as well , the agency said , were micronutrients for up to 20,000 children and water storage materials airlifted through Djibouti from UNICEF 's supply center in Denmark . Also Friday , the U.N. High Commissioner for Refugees said that about 900 refugees from Yemen have arrived in the Horn of Africa . Many more are reportedly trying to make the trip but are hampered by fuel shortages and high fees by boat operators . `` UNHCR is extremely concerned about the dangers for anyone trying to flee across the Red Sea and Gulf of Aden , where there are no search and rescue operations , '' the agency said in a statement . `` Last year , 246 lives were reported lost in sea crossings to Yemen . UNHCR appeals to all ships in the area to be extra vigilant and assist any boats in distress . We also ask that countries with vessels in waters near Yemen -- including surveillance and anti-piracy vessels -- instruct their ships to help with rescues . '' It said that , as demand increases , the boats attempting the dangerous crossing are likely to become more crowded -- a crossing that has historically been made in the other direction , by people fleeing Africa in favor of Yemen . Many Yemenis are attempting the trip in rickety fishing boats . One family told CNN the crossing was `` a window into hell . '' And underscoring the increasing toll being exacted by the conflict in Yemen , the World Health Organization said Friday that at least 643 people have been killed in the country since the fighting escalated three weeks ago . But it acknowledged that the number was almost certainly an underestimate . `` As of 6 April 2015 there have been a total of 643 deaths and 2,226 injuries , '' the WHO , the health arm of the United Nations , said in a statement . `` Casualty estimates are likely to change in the coming days as additional cases are verified and reported . '' The figures cover the period from March 19 to April 6 . They include , however , only deaths and injuries verified by a health facility . Other deaths and injuries have undoubtedly occurred . Security in the country , which is on the Arabian Peninsula , deteriorated sharply last month when Houthi rebels advanced on Sanaa and the port city of Aden , forcing President Abdu Rabu Mansour Hadi to flee the country . Since then , Saudi Arabia has launched airstrikes meant to halt the advance of the Houthis . In at least one case , according to Houthi sources , one of those strikes hit a school .
U.N. agency says 900 refugees from Yemen have arrived in Horn of Africa , asks ships in area to be vigilant . WHO : At least 643 people have been killed , more than 2,000 injured in Friday . UNICEF : Aid includes medical supplies for up to 80,000 people and more airlifts are planned .