More than 50 State Department diplomats have signed an internal memo critical of U.S. policy in Syria, calling for military strikes against President Bashar al-Assad's government to stop its persistent violations of a civil war ceasefire.
The "dissent channel cable" was signed by 51 mid- to high-level State Department officers advising on Syria policy.
It calls for "targeted military strikes" against the Syrian government in light of the near-collapse of the ceasefire brokered earlier this year, the Wall Street Journal reported, citing copies of the cable it had seen.
U.S. Secretary of State John Kerry, visiting Copenhagen, told Reuters on Friday: "It's an important statement and I respect the process, very, very much. I will … have a chance to meet with people when I get back [to Washington]."
He said he had not seen the memo.
Military strikes against the Assad government would represent a major change in the Obama administration's policy of not intervening directly in the Syrian civil war, while calling for a political transition that would see Assad leave power.
Such strikes would put the United States on a collision course with Russia, which is backing Assad with air strikes, equipment, training and military advice.
In Moscow, Kremlin spokesman Dmitry Peskov said he had only seen media reports about the memo, but said: "Calls for the violent overthrow of authorities in another country are unlikely to be accepted in Moscow.
"The liquidation of this or some other regime is hardly what is needed to aid the successful continuation of the battle against terrorism. Such a move is capable of plunging the region into complete chaos."
One U.S. official, who did not sign the cable but has read it, told Reuters the White House remained opposed to deeper American military involvement in Syria.
The official said the cable was unlikely to alter that, or shift Obama's focus from the battle against the threat posed by the Islamic State militant group.
Pressure on Assad
A second source who had read the cable said it reflected the views of U.S. officials who have worked on Syria, some for years, and who believe the current policy is ineffective.
"In a nutshell, the group would like to see a military option put forward to put some pressure … on the regime," said the second source, who spoke on condition of anonymity.
While dissent cables are not unusual, the number of signatures on the document is large.
"That is an astonishingly high number," said Robert Ford, who resigned in 2014 as U.S. Ambassador to Syria over policy disagreements and is now at the Middle East Institute, a Washington think tank.
"For the last four years, the working level at the State Department has been urging that there be more pressure on Bashar al-Assad's government to move to a negotiated solution," to the civil war, he said.
Ford said this was not the first time the State Department has argued for a more activist Syria policy. In 2012, Secretary of State Hillary Clinton proposed arming and training anti-Assad rebels. The plan, which had backing from other Cabinet officials, was rejected by President Barack Obama and his White House aides.
The dissenting cable discussed the possibility of air strikes but made no mention of adding U.S. ground troops to Syria. The United States has about 300 special operations forces in Syria carrying out a counter-terrorism mission against Islamic State militants but not targeting the Assad government.
"We are aware of a dissent channel cable written by a group of State Department employees regarding the situation in Syria," State Department spokesman John Kirby said.
"We are reviewing the cable now, which came up very recently, and I am not going to comment on the contents."
Kirby said the "dissent channel" was an official forum that allows State Department employees to express alternative views.
Central Intelligence Agency Director John Brennan told a congressional hearing on Thursday that Assad was in a stronger position than he was a year ago, bolstered by Russian air strikes against the moderate opposition.
Brennan said Islamic State's "terrorism capacity and global reach" had not been reduced.
The names on the memo are almost all mid-level officials, many of them career diplomats, who have been involved in Syria policy over the past five years, at home or abroad, the New York Times said.