Tony Blair has called on the west to stop "wringing our hands" as he endorsed intervention against the regime of Bashar al-Assad and warned governments against ostracising the military dictatorship in Egypt.

In his first intervention since the chemical weapons attack last week, the former prime minister said the west should not be neutral in protecting Syrians from the Assad regime and "affiliates of al-Qaida" seeking to exploit the instability.

Blair made his remarks in a Times article in which he said the west should acknowledge the threats in Syria and Egypt.

He wrote: "Western policy is at a crossroads: commentary or action; shaping events or reacting to them. After the long and painful campaigns in Iraq and Afghanistan, I understand every impulse to stay clear of the turmoil, to watch but not to intervene, to ratchet up language but not to engage in the hard, even harsh business of changing reality on the ground. But we have collectively to understand the consequences of wringing our hands instead of putting them to work."

Blair, who was humiliated by Assad during a trip to Damascus after the 9/11 attacks, when the Syrian president likened Palestinian suicide bombers to the Free French, said it was time to intervene against the regime.

"I hear people talking as if there was nothing we could do: the Syrian defence systems are too powerful, the issues too complex and, in any event, why take sides since they're all as bad as each other?" he wrote. "It is time we took a side: the side of the people who want what we want; who see our societies for all their faults as something to admire; who know that they should not be faced with a choice between tyranny and theocracy."

Blair, who was close to the former Egyptian president Hosni Mubarak, also warns it would be a grave strategic error to ostracise the government that has overthrown former president Mohammed Morsi.

He wrote: "You can rightly criticise actions or overreactions of the new military government but it is quite hard to criticise the intervention that brought it into being … We should support the new government in stabilising the country, urge everyone, including the Muslim Brotherhood, to get off the streets, and let a proper and short process to an election be put in place with independent observers."

Blair acknowledged that people were acting cautiously after the Iraqi intervention. He wrote: "In this struggle, we should not be neutral. From the threat of the Iranian regime to the pulverising of Syria to the pains of the Egyptian revolution, from Libya to Tunisia, in Africa, central Asia and the far east, wherever this extremism is destroying the lives of innocent people, we should be at their side and on it.

"I know as one of the architects of policy after 9/11 the controversy, anguish and cost of the decisions taken. I understand why, now, the pendulum has swung so heavily the other way. But it is not necessary to revert to that policy to make a difference. And the forces that made those interventions in Iraq and Afghanistan so difficult are of course the very forces at the heart of the storm today."