Activists say "tens" of people of were killed and wounded in a Syrian government airstrike on a livestock market in an Islamic State stronghold.

Two activist-run monitoring groups, the Britain-based Syrian Observatory for Human Rights and the Local Coordination Committees, said the attack occurred Tuesday in the far eastern village of Khansaa, near the Syria-Iraq border. Khansaa is held by the Islamic State militant group.

The monitoring groups did not give precise death tolls. The Observatory said "tens" were killed and wounded.

The groups said government aircraft dropped so-called barrel bombs -- crude canisters laden with explosives -- on the market. Such bombs cannot be precisely targeted and activists say they have killed thousands of civilians.

The U.N. estimates that Syria's four-year conflict has killed over 220,000 people.