* General Salim Idriss seen in video footage in Latakia
* Islamist hardliners overshadow moderate rebel groups (Adds U.N. comment)
BEIRUT, Aug 12 (Reuters) - The head of the rebel Free Syrian Army has visited the coastal province of Latakia, according to video footage, a show of force in President Bashar al-Assad's family's home province.
Several villages in Latakia, which is a stronghold of Assad's Alawite sect, have been overrun by Sunni Muslim insurgents over the past few days.
General Salim Idriss, who leads the rebel Supreme Military Council, was shown in a video uploaded to the Internet on Sunday wearing casual dress and a shoulder-strapped gun holster and standing outside with mountains in the distance.
Speaking to rebels, he said he was in Latakia to see the "important successes and victories that our revolutionaries have gained on the coastal front".
Reuters cannot independently verify reports due to severe security and reporting restrictions.
Idriss' forces are backed by the West, but the Latakia offensive is being led by two al Qaeda-linked groups who have killed hundreds of people this month and driven hundreds more to seek refuge on the Mediterranean coast.
Underfunded and fragmented, Idriss' men have been overshadowed by these hardline groups and some more moderate rebel leaders have been killed in power struggles with al Qaeda affiliates that include foreign fighters.
The U.N. Office for the Coordination of Humanitarian Affairs has received reports over the past two days that "indicate more than 3,000 families have been displaced from around 30 villages around Latakia," U.N. spokesman Eduardo del Buey said on Monday.
"The Syrian government has opened three shelters but reports indicate that 80 percent of the displaced people are staying with relatives and host communities inside Latakia," he said.
One extremist group, the Islamic State of Iraq and the Levant, issued a statement on Sunday saying its militants were now "a stone's throw from Qurdaha", the Assad family's hometown. It said the militants had fired rockets into the town.
The rebel advance into Alawite territory is a major gain for Assad's foes after months of setbacks during which they lost ground around the capital Damascus and the central city of Homs.
Combined with a steady fight back in the southern province of Deraa, it highlights the challenge Assad faces in trying to restore his authority across Syria after two years of conflict that has killed 100,000 people and fragmented the country.
Assad controls much of southern and central Syria, while rebels hold northern areas near the Turkish border and along the Euphrates valley towards Iraq. The northeast corner is now an increasingly autonomous Kurdish region.
(Reporting by Oliver Holmes in Beirut and Michelle Nichols at the United Nations, editing by Elizabeth Piper and Cynthia Osterman)