Syrian President Bashar al-Assad is to blame for the civil war engulfing his country and the West should not talk to him just because Islamic State (IS) is "even worse", German Chancellor Angela Merkel's foreign policy adviser said on Tuesday, Nov 11, according to Reuters.

IS militants have seized swathes of territory in both Syria and Iraq and a U.S.-led coalition is targeting them in air strikes, providing some respite for Assad's forces and prompting some to suggest a possible rapprochement with the president.

"(Despite) the fact that maybe now there is an organization - ISIS - that with regard to humanitarian and human rights violations is even worse than Assad, we shouldn't consider Assad now somebody who can be an interlocutor and somebody whom we should work with," said Christoph Heusgen, Merkel's chief adviser on foreign and security policy.

ISIS is another name for Islamic State.

"We must not forget it is Assad who is to blame for hundreds of thousands of people who have been killed, millions of people who have been misplaced," Heusgen told a conference in Berlin.

Heusgen said there was a need for a political solution in Syria involving major regional powers such as Iran and Saudi Arabia, and he also urged Russia to use its influence with the president to end the civil war, which erupted in 2011.

"I see the Russian ambassador here (at the conference) and Russia has excellent relations to Assad, providing him with weapons, and I think there is somebody who could talk to him and tell him to come to his senses," Heusgen said.

Russia is Assad's biggest backer and has urged Western and Arab governments to engage with him to combat IS. Moscow objects to the U.S.-led strikes on IS targets in Syria, saying they should first be agreed with Assad.