The Central Military Media Center, an outlet affiliated with the Syrian military, said Syrian troops and allied fighters have begun entering the town.
The two outlets said earlier that Syrian troops had linked up with Iraqi forces across the border. The Syrian Observatory for Human Rights, however, disputed this account, saying some fighting continued across the town.
In Syria, the end of major battle operations against Islamic State may only prefigure a new phase of the war, as the rival forces that have seized territory from the jihadis square off.
A USA -backed coalition has supported a rival campaign in Syria by the Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab militias that have pushed Islamic State from much of the country's north and east.
Prime Minister Haidar al-Abadi announced on Friday the liberation of Qaim "in record time" - just over a week since announcing the offensive targeting the last Iraqi remnants of the self-styled caliphate IS declared after rampaging across Iraq and Syria in 2014.
Croft cautioned that US operations against the terrorist group will continue for some time as ISIS morphs into an insurgent like force that is likely to try to exploit desert areas in Iraq and Syria. Later the same day, Iraqi forces took al-Qaim, across the border. Pro-government forces were also mobilized last month to check a failed Kurdish bid for independence. Both the Syrian and Iraqi militaries, along with their allied militias and respective worldwide sponsors, have largely defeated ISIS, but parts of Syria remain under rebel and Kurdish control.