Kerry says US diplomats' call to bomb Assad 'a well-written argument'

US Secretary of State John Kerry said on Monday he had read a memo from a group of frustrated diplomats urging strikes against the Syrian government and found it "very good".

The "dissent cable" became public last week after 51 serving US officials signed a call for direct US military action to force Bashar al-Assad's government to negotiate for peace.

The memo was seen as a criticism of President Barack Obama's cautious approach, but the "dissent channel" is an approved mechanism for diplomats opposed to official policy.

The State Department has already said the dissident mid-level staff will not face retribution for speaking out, and on Monday their boss Kerry appeared to signal support for their views.

Asked at a public event for college students whether he had read the dissenting memo, which was leaked to the press last week, Kerry said: "Yes. It's very good. I'm going to meet with them."

Afterwards, Kerry's spokesman John Kirby said the secretary was not publicly endorsing the policy change suggested by the memo but had found it "a well-written argument".

Asked whether Kerry might take the suggestion of US strikes to Obama, Kirby said "obviously, whatever views, advice or counsel he presents to the president needs to remain private".

"But then also ... he has made no bones about the fact that he is not content with the status quo in Syria. We are not content with the status quo in Syria," he added.

Kerry has remained publicly loyal to Obama as the five-year-old carnage in Syria continues, pushing an improbable joint US-Russian plan to lure Assad and the rebels to the negotiating table.

But Kerry's equanimity in the wake of the dissent cable - a somewhat unusual if not an unprecedented rebuke from frontline staff - supports suggestions that he is frustrated.

Dozens of US diplomats have said their country should launch military strikes against the Syrian government, breaking ranks with Obama's policy on the war.

The so-called "dissent channel" cable urges attacks against Bashar al-Assad's government for its persistent violations of a shaky ceasefire aimed at bringing an end to the five-year conflict.

The cable, signed by 51 working-level diplomats, calls for "a judicious use of stand-off and air weapons", according to the New York Times, and lays bare the divisions in Washington policy circles.

Russia on Friday said the thrust of the message was "obviously at odds with UN resolutions" on Syria.

The State Department cable says Assad's continued violation of a countrywide partial ceasefire - a cessation of hostilities - that was negotiated in February, meant a political settlement was untenable, the Times reported.