German Chancellor Angela Merkel has said only with the help of Russia could Syria's civil war be brought to an end.

"For years we have known there can be a solution only with the help of Russia," Der Spiegel quotes her as saying on in a Thursday speech.

Faultlines between Western partners' positions on the conflict in Syria come amid Reuters' reports that Iranian forces are preparing to join Assad's forces in a major land offensive. Earlier, Moscow vowed to back the Syrian army in its "lawful fight against terrorist groups". Washington was not immediately able to confirm.

Talks are due between Russian President Vladimir Putin and his French counterpart Francois Hollande over Russia's air campaign on targets it says are Islamic State (IS) and other opposition groups.

The White House believes Russian strikes are randomly hitting opposition forces, rather than Islamic State. It was warned that "indiscriminate military operations against the Syrian opposition" are "dangerous for Russia" and could only "prolong the sectarian conflict inside Syria, if not make that conflict indefinite."

Russian Foreign Minister Sergey Lavrov, however, said on Thursday his country had "the same position" as the United States on fighting terrorist organizations like IS and the Nusra Front.

In his words, Russia did not consider the Free Syrian Army to be a terrorist organization and added Moscow considered it to be part of the political solution for the country.

According to President Hollande, quoted by the BBC, the strikes "regardless of who is carrying them out," should only "target Daesh and not other groups." Da'esh is an Arabic acronym for IS that the French government has officially adopted, vowing it will not use "IS" to avoid giving legitimacy to the groups.