The overnight strikes killed "a number of civilians and soldiers, wounded others and caused significant damage to public and private property", the Syrian military said in a statement.

"The occupation of parts of Syrian territory by US forces cannot continue," it added, affirming the army's "determination to liberate all Syrian territory from terrorism and occupation".

The United States blamed Sunday's drone attack in Jordan on Iran-backed groups, but did not strike inside Iranian territory, with both Washington and Tehran seemingly keen to avoid all-out war.

The United States has some 900 troops in Syria and 2,500 in neighbouring Iraq as part of an international coalition against the Islamic State group, a jihadist organisation that once controlled swathes of both countries.