benghazi libya east libyan force say launch air strike islamic state fighters militants make incursions south east former coastal stronghold sirte jihadist group grow bold recent weeks set temporary checkpoints attack local force take village mosque lead prayers muslim holiday eid al-adha libyan officials say increase activity raise concern islamic state could regroup around sirte drive december local force u.s. air campaign militants kill nearly seven-month battle unknown number flee desert south west sirte lie center libya mediterranean coastline divide line regions control rival libyan factions force loyal eastern-based commander khalifa haftar say carry air strike sunday militants area taqrift sirte town zillah 306 km 190 miles south east area close oil field previously damage islamic state attack haftar libyan national army lna force port city misrata lead campaign sirte last year say mount frequent patrol monitor islamic state movements areas control lna misratan brigade opposite side conflict develop nato-backed uprise topple libyan strongman muammar gaddafi 2011. islamic state exploit turmoil establish foothold libya take complete control sirte 2015 use base hundreds foreign fighters main loose alliances libya accuse allow islamic state space operate order advance military end misratan force align u.n.-backed government tripoli complain receive little support try prevent jihadists regroup islamic state militants step presence several settlements east sirte say ibrahim mlaitan head security sirte municipality include enter local mosque preach sermon last friday say set checkpoints last 10 minutes leave move around freely towns desert mlaitan say eastern military officials deny report islamic state take control one villages um qandeel military source acknowledge militants set checkpoints fleet night visit terrorist organization daesh islamic state time time try enter coastal areas desert regions carry kidnappings civilians conduct surveillance say lna spokesman ahmed al-mismari libyan force attack islamic state near former stronghold