tunis/tripoli u.n. agencies say monday try provide urgent help large number migrants hold strand smuggle hub sabratha rival factions battle control city least 4,000 migrants include pregnant women newborn baby unaccompanied children transfer informal camp house hangar city since clash end friday international organization migration iom say u.n. refugee agency unhcr say 6,000 hold informal sit hundreds migrants leave sabratha arrive zuwara 25 km 15 miles west foot along beach say sadeeq al-jayash head zuwara emergency committee come walk group ... example various group come sunday 50 100 200 night say jayash 1,700 migrants currently zuwara desperate need help say sabratha common point departure mostly sub-saharan african migrants try cross mediterranean boat libya number cross drop sharply july arm group strike deal officials u.n.-backed government tripoli block departures pressure italy european union member state set three weeks fight among rival factions leave least 43 dead 340 wound accord new health ministry toll end withdrawal arm group migrants since round hold sit group control local officials say seriously concern large number migrants catch recent developments sabratha othman belbeisi iom libya chief mission say statement migrants send detention center elsewhere western libya nominally control tripoli government iom officials say center house 5,000 migrants risk overwhelm new arrivals condition center often dire abuse widespread alternatives detention must find migrants libya meantime iom continue provide direct humanitarian health psychosocial assistance meet urgent need thousands migrants affect belbeisi say local source previously say estimate 10,000 migrants hold sabratha area head sabratha department counter illegal migration tell reuters saturday help badly need migrants receive food water six days unhcr say approach libyan authorities ensure refugees among migrants free detention u.n. assist thousands migrants libyan smuggle hub