(CNN) -- Prominent U.S. conservatives want the Obama administration to "take immediate action" against the Syrian regime, including "no-go zones" for President Bashar al-Assad's military and "self-defense aid" to resistance forces.
Fifty-six foreign policy experts and former U.S. government officials signed a letter dated Friday calling for proactive U.S.-led steps against the government. It comes as Syrian citizens and activists plead for world powers to help stop the government's bloody crackdown.
They include Karl Rove, the former Bush administration adviser; Paul Bremer, in charge of the U.S. occupation in Iraq after the 2003 invasion; R. James Woolsey, former CIA chief; Robert McFarlane, former Reagan national security adviser, and Dan Senor, a former Bremer adviser and spokesman for the Coalition Provisional Authority in Iraq.
The letter can be found on the Foreign Policy Initiative website.
"We believe that the United States cannot continue to defer its strategic and moral responsibilities in Syria to regional actors such as the Arab League or to wait for consent from the Assad regime's protectors, Russia and China," the letter said.
Russia and China have vetoed strong action against the al-Assad regime at the U.N. Security Council.
The letter calls for Syrian safe zones and no-go zones for al-Assad's forces around "Homs, Idlib, and other threatened areas, in order to protect Syrian civilians."
"The United States should work with like-minded countries like Turkey and members of the Arab League in these efforts," the letter said.
The group wants to "establish contacts" with the Free Syrian Army, the fledgling resistance force of military defectors. It called for a "full range of direct assistance, including self-defense aid to the FSA" and wants to do so with Middle East and European allies.
The letter calls for improving "U.S. coordination with the political opposition groups" and to "provide them with secure communications technologies and other assistance that will help to improve their ability to prepare for a post-Assad Syria."
It wants the administration to work with lawmakers to impose "crippling U.S. and multilateral sanctions" on the Syrian government, specifically the energy, banking and shipping sectors.
The letter cites the Syrian government's bloody siege in the city of Homs, and says the regime "poses a grave threat to national security interests."
One Syrian activist group, the Local Coordination Committees of Syria, says more than 8,500 people have died in the unrest, now in its 12th month.
It notes that Syria has maintained "a strategic partnership with the terror-sponsoring government of Iran, as well as with Hamas and Hezbollah" and it has "facilitated the entry of foreign fighters into Iraq, who killed U.S. troops."
It says foreign powers intervened in support of the al-Assad regime, citing Russia's supply of arms and supplies, and reports of Iran and Hezbollah operating in Syria.
"The lack of resolve and actions by the responsible members of the international community is only further emboldening the Assad regime," the letter said.
"Unless the United States takes the lead and acts, either individually or in concert with like-minded nations, thousands of additional Syrian civilians will likely die, and the emerging civil war in Syria will likely ignite wider instability in the Middle East."
The United States, the European Union, the Arab League and Turkey have initiated a range of sanctions against Syria.
The Obama administration has also denounced al-Assad's regime
"Assad has no right to lead Syria, and has lost all legitimacy with his people and the international community," Obama said February 4.
"A Syria without Assad could be a Syria in which all Syrians are subject to the rule of law and where minorities are able to exercise their legitimate rights and uphold their identities and traditions while acting as fully enfranchised citizens in a unified republic."
Despite a General Assembly non-binding resolution endorsing an Arab League plan for al-Assad to step down, world powers haven't been able to stop the bloodshed.
Secretary of State Hillary Clinton Friday said the United States has not been "deterred" by Security Council vetoes and is moving forward with a group called the Friends of Syria, a coalition of Arab, Western and others countries.
The group, which will meet Friday in Tunisia, was formed after Russia and China stood in the way of a Security Council measure to deal with Syria.
"We are doing all we can to determine ways forward, to strengthen the opposition, to help them convey to the entire Syrian population that they are seeking an inclusive, peaceful, democratic transition," Clinton said.
Victoria Nuland, State Department spokeswoman, said Friday that the president doesn't rule out "any option."
"That said, we do not think that more guns into Syria ... or international intervention in Syria is the right answer. We don't think further militarizing the situation is going to bring peace and stability and a democratic transition to the people of Syria," she said.
"We are instead focused on strengthening and unifying the opposition so that it is prepared and ready for that day when Assad cedes power, which he will eventually, so that the Arab League proposal or something like it can be implemented. And we're in the short term very focused on strengthening our humanitarian support to those suffering in Syria."