BEIRUT: The Islamic State group claimed responsibility Friday for triple suicide bombings in northern Syria that killed at least 26 people and wounded 90, underscoring its ability to launch attacks in areas that it has lost to rival groups.

The extremist group said in a statement posted online that the attacks in the predominantly Kurdish province of Hassakeh targeted offices of the main Kurdish militia known as the YPG.

The attacks in the town of Tal Tamr occurred late Thursday.

Read more: 22 killed in Syrian truck bomb attack: Monitor

Syrian state media and an activist group said the blasts targeted a medical center and a busy market.

Syrian State TV and IS said on Friday the blasts killed 60 people and wounded 90 while the Britain-based Syrian Observatory for Human Rights said they killed 26, including four Assyrian Christians. The observatory said 120 people were wounded.

Tal Tamr, once inhabited by Assyrian Christians, is now an overwhelmingly Kurdish town where the main Kurdish fighting force in Syria - People's Protection Units (YPG) - is in control. The group is the most effective fighting force against the IS.

Also Friday, the observatory and the Local Coordination Committees (LCC), another opposition group that tracks the civil war in Syria, reported that warplanes struck small, primitive oil refineries used by villagers in the eastern province of Deir el-Zour. The observatory said the warplanes were believed to be Russian.

The LCC said seven people were killed and others were wounded while the observatory said dozens were killed or wounded in the attack on the villages of Zgheer and Kasra.

The Russians and the US-led coalition have been targeting oil facilities in an attempt to deprive IS of one of its main sources of income.

Read more: US air strikes target oil tankers, rigs in bid to disable IS funding

In February, IS overran much of Khabur and kidnapped at least 220 Assyrian Christians.

Also read: Christians among 230 kidnapped by IS in Syria

But Kurdish fighters from YPG subsequently recaptured the area, and dozens of the hostages have been released in recent months.

On Wednesday, some 25 Assyrians, including two children, were freed by IS, according to the Assyrian Human Rights Network.

Related: IS frees 10 kidnapped Syrian Christians

Elsewhere, the observatory said at least 12 people, seven of them children, were killed in rebel fire on government-held parts of Aleppo city in the past 24 hours.

This week, rebels have stepped up fire into western Aleppo, killing dozens.

Also read: Syrian army launches Aleppo offensive with Iranian support