* Syrian soldiers celebrate inside Crusader castle
* Securing western Homs cuts rebel supply routes
By Firas Makdesi
CRAC DES CHEVALIERS, Syria, March 21 (Reuters) - Standing at the gate of a Crusader castle captured from insurgents less than 24 hours before, a Syrian army officer declared on Friday that forces loyal to President Bashar al-Assad were now in control of the western half of Homs province.
The securing of the area follows three months of gains by government forces against opposition groups and serves two aims - cutting rebel supply routes from Lebanon, which borders Homs, and securing a highway that connects the capital to the coast.
Controlling this road is especially important for Assad as it is used to transport chemical weapon agents to be shipped out and destroyed under an international agreement.
Syrian authorities, battling a three-year-long insurgency against Assad, blame security problems for being months behind schedule, citing attempted attacks on convoys carrying chemical agents last month.
Multiple army checkpoints punctuate the 160 km (100 mile) drive from Damascus to the Crac des Chevaliers fortress - a UNESCO World Heritage site - but no sign of opposition forces.
The Syrian army convoy and journalists passed by several towns in the Qalamoun mountain range that were also recently captured by the army.
Syrian soldiers raised the national flag on the battlements of Crac des Chevaliers on Thursday after a three-month seige. Its fall followed the army's retaking on Sunday of Yabroud - one of the last rebel-held towns along the Damascus-Homs highway.
"We are in complete control of the western Homs countryside," the officer told Reuters, without giving his name.
His soldiers walked around the 900-year-old castle that T.E. Lawrence, the British army officer who fought with Arab warriors against Ottoman rule in World War One, called the "best preserved and most wholly admirable castle in the world".
The hilltop fortress suffered mortar hits last year as rebels sheltered behind its thick stone walls, built for battles hundreds of years ago. The outer walls appeared intact and only minor damage inside, with some chipped stones and bullet holes.
Insurgents had left beds, plates and books inside the medieval arched rooms of the castle.
The officer said the rebels there were foreign extremists from "Saudi, Palestine and Lebanon." The insurgents fled on Thursday morning but were ambushed by the army. Some made it to Lebanon.
More than 140,000 people have been killed in the Syrian conflict, which has become increasingly sectarian as rival regional powers have backed either Assad, a member of the Shi'ite offshoot Alawite sect, or the majority Sunni rebels.
With western Homs in government hands, nearly all Syrian areas bordering Lebanon are unsafe for rebels. Lebanese Shi'ite militant group Hezbollah, which says Syrian rebels endanger Lebanon, have helped Assad in his fight to preserve four decades of dynastic rule.
But Hezbollah's intervention has been followed by car bombs in Shi'ite residential areas of Lebanon, rocket attacks on Shi'ite towns and a flood of refugees and Sunni rebels into the country, causing outrage from Hezbollah's critics who say it has no mandate to enter a foreign war. (Writing by Oliver Holmes; Editing by Angus MacSwan)