LONDON: British Foreign Minister Boris Johnson Wednesday called for the mistakes of the Iraq war to be avoided in finding a solution to the Syrian conflict, ahead of talks with the country's opposition.

Johnson called for the removal from power of Syrian President Bashar Assad, arguing that it would be possible to avoid the turbulence which followed the ousting of Iraqi President Saddam Hussein in 2003.

"Why should the same not happen again?... Assad is not a strongman but a frighteningly weak leader who can never again hold his country together - not after the slaughter he has engaged in," the foreign minister wrote in The Times newspaper.

Johnson accused Assad of "barbaric military tactics" in the ongoing conflict and criticized Russia's "seemingly indefensible conduct" of backing the Syrian leader.

"The entire international community is committed, at least in principle, to getting rid of the Syrian dictator. Even the Russians have accepted that there must be political transition.

"But then the Russians are also employing their military muscle to prevent him from losing and to keep him in power," Johnson wrote.

The foreign minister's comments were published ahead of a meeting in London with Syria's opposition High Negotiations Commission, which was expected to unveil its framework for political transition later Wednesday.

Johnson said the proposals would not seek to sweep away state structures: "That was (one of) the mistakes in Iraq, and it will not be repeated."

He said plans would include a six-month negotiating phase between the regime and the opposition.

The subsequent 18 months would see Syria governed by a transitional body, made up of opposition figures, current government representatives and members of civil society.

The five-and-a-half-year conflict has forced more than 4.8 people to flee Syria, according to figures from the United Nations refugee agency UNHCR.