Britain must protect the Syrian opposition from being "exterminated", William Hague said as he warned that the crisis is "on a trajectory to get worse".
The Foreign Secretary said the only way of securing a political solution in the conflict is to ensure that moderates opposing Bashar Assad's regime are not destroyed.
He warned there are "no palatable options" as he again insisted no decision had been taken over arming the rebels "at this stage".
Mr Hague told the BBC Radio 4 Today programme: "There is, in the end, only a political solution to it. A military conquest of either side by the other side would lead to the collapse of the Syrian state.
"Our fear is we are only going to get a political solution to this crisis if the opposition, the moderate sensible parts of the opposition, can't be destroyed. Therefore, they do need assistance of various kinds."
"We don't rule any option out. We shouldn't rule any option out because who knows how serious this crisis will become, how it will develop over the coming months or years, indeed," he added.
"There are no palatable options, I want to be clear with the whole country, there are no easy options at all. Of course it's not easy to take any decision to send arms to a conflict. It's also not easy to take a decision to allow people to be killed who are faced by much superior arms and who may be driven to radicalism and extremism by being placed in that situation."
Mr Hague conceded there are "more than two sides" in the conflict after London mayor Boris Johnson publicly warned against arming the rebels, suggesting the weapons could end up in the hands of "al Qaida-affiliated thugs".
The Foreign Secretary said: "There certainly are extremists. The complexity of this situation is there are more than two sides.
"I have had many meetings with opposition leaders who are not that type of opposition leader, who are sincere in my view and the view of (US secretary of state) John Kerry and many other Western foreign leaders about their commitment to a future democracy in Syria, to dealing with the stockpiles of chemical weapons, to making sure that minorities are properly represented and not persecuted in Syria. Their commitment to that is sincere."