Syrian Fighting Has Blocked Humanitarian Aid, Health Officials Say BEIRUT, Lebanon - Syrian forces bombarded the city of Homs for a sixth day in a row on Friday, while government soldiers backed by Hezbollah fighters clashed with rebels on the outskirts of the city's besieged Khalidiya neighborhood amid warnings from international health officials that fighting was increasingly preventing humanitarian aid from reaching those most in need. Government forces have trained their sights on Homs and the northern city of Aleppo in recent weeks since they recaptured the strategic border town of Qusayr last month. Antigovernment activists have said the government was aided in the battles by fighters from Hezbollah, the Lebanese Shiite militant group. The group has not confirmed that, saying only that it would go where it was needed to fight off the insurgency against Syria's president, Bashar al-Assad, which Hezbollah leaders say threatens Lebanon and the region. On Friday, clashes intensified near Khalidiya, which the army has been trying to storm for weeks, according to the Syrian Observatory for Human Rights, a Britain-based watchdog group with a network of activists in Syria. While the Syrian Army holds large sections of Homs, rebels continue to hold out in a few central neighborhoods. The sustained violence has left the civilian population in dire need of humanitarian assistance, prompting the Syrian National Coalition, the main exile opposition body, to release a statement on Friday asking the United Nations to provide immediate aid. "The areas under attack in Homs have been cut off from the rest of the world and suffer an urgent shortage of medicine and staple foods," the dispatch read. Restrictions put in place by the Syrian authorities in recent weeks have increasingly blocked delivery of medicine and medical supplies around the country, even to areas under government control and even as health needs are escalating for people trapped in two years of conflict, the World Health Organization warned on Friday. "The main problems are to get medicines and medical supplies out from Damascus," the Syrian capital, Elizabeth Hoff, the agency's representative in Damascus, said in a telephone interview. Ms. Hoff said that there was an acute lack of dialysis treatments for more than 5,000 patients, and that there were reports of doctors being forced to deliver babies by Caesarean section without proper anesthetics. The health agency's warning was one of several alarms sounded by United Nations organizations on Friday. The human rights office expressed concerns for the fate of several thousand civilians caught in parts of Homs and urged all parties to allow civilians to leave the area without fear of persecution or violence. The United Nations" Rome-based food agencies warned that Syrian crop production had slumped as a result of the disruption and population displacement caused by the war, leaving a quarter of the population unable to produce or buy sufficient food. The World Food Program said it was providing food support for 2.5 million people and was trying to put in place the logistical capacity to support four million people by October. Public health experts said the national health infrastructure was suffering under the pounding and politics of the conflict. The government has introduced cumbersome procedures requiring agencies to obtain "facilitation" letters to authorize movement of medical supplies, Ms. Hoff said. And in recent weeks officials had largely stopped issuing them, citing security concerns and fears the supplies would end up with the rebels, she said. Ms. Hoff said that the Syrian government had directed that all medical supplies be sent to the Health Ministry, and that its warehouses were brimming with supplies that had not been distributed. The humanitarian warnings came as members of the Syrian National Council convened a two-day meeting in Istanbul to elect new leadership and bridge internal divisions - part of a continuing effort to convince Western backers that it can be trusted with distributing lethal aid to moderate elements in the insurgency.