Syrian rebels captured a major air base in the north of the country on Tuesday after months of fighting, depriving President Bashar Assad's forces of one of their main posts near the border with Turkey, activists said. State TV denied that the base had fully fallen.

The Britain-based Syrian Observatory for Human Rights said Mannagh helicopter base fell nearly 24 hours after rebels, led by al-Qaida-linked militants, launched an all-out offensive against it.

Another activist group, the Aleppo Media Center, said rebels finally captured it before dawn. Videos purportedly from the battlefield showed rebels inspecting captured helicopters.

Syria's state TV said troops are still defending the air base, adding that rebels "suffered very large losses around and inside the airport."  Quoting an unnamed Information Ministry official, the TV said "the heroes of our armed forces at Mannagh air base and nearby areas are confronting terrorists with great courage."

Mannagh, in the north of Aleppo province, is deep inside territory dominated by the Syrian opposition. Rebels have been trying since last year to capture it, but faced strong resistance from defenders.

Rebels seized part of it in June, and since then its fall has been widely expected. The air base is the largest to fall in rebel hands since opposition forces captured the Taftanaz base in the northern province of Idlib in January.

The Observatory said the final assault on Mannagh was led by members of the al-Qaida-linked Islamic State of Iraq and the Levant. It began early Monday when a Saudi suicide attacker blew up his vehicle outside the command center of the sprawling compound.

It said the rebels then began advancing, capturing vehicles and buildings inside the base. It did not say how many government troops were killed but said at least 10 rebels, including foreign fighters, died in the fighting.

The Observatory added that rebels took prisoner a number of government troops.

Syria main's opposition bloc, the Western-backed Syrian National Coalition, congratulated Syrians on the capture of the base. It said rebels "fully liberated the Mannagh air base and will transfer it from a regime tool for oppression to a minaret of liberation."

Amateur videos released by activists showed rebels walking inside the base amid damaged helicopters. Several tanks and armored personnel carriers could also be seen in the base.

"Thanks to God, the airport was fully liberated and here are the spoils," said the narrator as rebels could be seen standing in front of an armored personnel carrier and green wooden ammunition boxes.

The videos appeared genuine and corresponded to other Associated Press reporting on the events depicted.

The capture of Mannagh could now free hundreds of opposition fighters to reinforce other fronts, including the sieges of the nearby Shiite-majority regime-held towns of Nubul and Zahra.

Syria's conflict has taken on an increasingly sectarian tone in the last year, pitting predominantly Sunni Muslim rebels against members of Assad's Alawite sect.

The fall of Mannagh followed the rebel capture of four villages in the Alawite heartland on the country's Mediterranean coast. Rebel victories have otherwise been comparatively rare in recent months, and Assad's forces have been on the offensive in the center of the country.

The Observatory reported heavy fighting in the coastal province Tuesday, saying rebels were able to capture another village, Khirbet Baz. The village is in the Jabal al-Akrad hills of the Latakia province.

Much of Latakia has been under the firm control of Assad's forces since the beginning of the conflict more than two years ago, but some areas, including Jabal al-Akrad, are close to rebel-held areas and have seen fighting.

The pro-government daily Al-Watan said rebels on Monday kidnapped Sheik Badreddine Ghazal, a prominent Alawite cleric in the region. The paper said he was taken from the village of Barouda, one of those captured by rebels earlier Monday.

A government official in Damascus confirmed Ghazal's abduction saying the cleric was "severely beaten" by his captors. The official, who spoke on condition of anonymity in line with regulations, did not give further details.

More than 100,000 people have been killed since Syria's conflict started in March 2011 as largely peaceful protests against Assad's rule. After opposition supporters took up arms to fight a brutal government crackdown on dissent, it turned into an armed uprising and later escalated into a civil war.