BEIRUT (Reuters) - A large truck bomb blast claimed by Islamic State killed nearly 50 people and wounded scores more in the northeastern Syrian city of Qamishli near the Turkish border on Wednesday, a monitoring group and state television reported.

The attack, which hit near a Kurdish security forces headquarters, was the deadliest of its kind in the city for years, the British-based Syrian Observatory for Human Rights said.

The blast, which took place early on Wednesday, killed at least 48 people. The death toll expected to rise because of the number of people seriously injured, the Observatory said. State media put the death toll at 44.

Kurdish forces control much of Hasaka province, after capturing vast areas from the jihadist group last year. The Kurdish YPG militia, which has proved the most effective partner for a U.S.-led coalition battling Islamic State, is also involved in fighting the extremists farther west, in Aleppo province.

Islamic State claimed responsibility for what it said was a suicide truck bomb attack, and added that it targeted Kurdish security forces. The group State has carried out a number of bombings in Qamishli, which is in Hasaka province, and in the provincial capital, Hasaka city.

State TV rolled footage purportedly from the scene of one blast, showing large-scale damage to buildings, vast amounts of rubble strewn across the road and plumes of smoke rising.

The explosion was so powerful it shattered the windows of shops in the Turkish town of Nusaybin, directly across the border. Two people were slightly hurt in Nusaybin, a witness said.

Islamic State has targeted Qamishli and the provincial capital, Hasaka city, in the past with bombing attacks. A suicide blast killed six members of the Kurdish internal security force, known as the Asayish, in April. In July, an Islamic State suicide bomb killed at least 16 people in Hasaka.

The YPG is now involved in a U.S.-backed offensive that has advanced against the jihadists further west near the Turkish border.

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The assault against Islamic State in the city of Manbij has put it under pressure, cutting off all routes out of the city. Fighters from the U.S.-backed alliance have in recent weeks made incremental advances as they try to flush out the remaining IS fighters in Manbij.

Territory that Islamic State controls in that area was a major supply route to the outside world via the Turkish-Syrian border, through which it moved weapons and fighters.

(This story has been refiled to fix typo in fourth paragraph)