* Ford says Assad government committed "massive" rights violations
* Says unwise to take Assad at his word on embracing peace plan
WASHINGTON, March 27 (Reuters) - The U.S. ambassador to Syria, Robert Ford, said on Tuesday he had received reports that armed Syrian opposition groups had engaged in human rights abuses as well as Syrian government forces, and had warned both sides against committing such acts.
Ford also expressed skepticism about reports that Syria had accepted the peace plan of U.N.-Arab League envoy Kofi Annan, saying it would be best to look for action, not words from Syrian President Bashar al-Assad.
"I have to tell you that my own experience with him (Assad) is you want to see steps on the ground and not just take his word at face value," Ford said.
The United States announced on Feb. 6 it was closing its embassy in Syria because of the worsening security situation there but Ford remains ambassador, working from Washington.
At a Capitol Hill hearing, Ford was asked about recent statements by the U.S.-based group Human Rights Watch that armed opposition groups in Syria had committed serious human rights abuses. It said these abuses included kidnapping, detention and torture of security force members and government supporters.
"We had reports like that last year, when some of the fighting in Homs became really serious," Ford said.
"We raised it even in Syria when my embassy was still open. We discussed it with some of the local revolution council representatives - who are themselves not members of armed groups, but certainly are in contact with them - and emphasized that they would be held to a standard on this if they wanted support from western countries," he said.
Ford said the United States had also raised the matter with the Syrian National Council, a Syrian opposition coalition, and he noted that last week the council issued a statement saying such abuses were against what they stood for.
Ford gave no details of reports he had received about human rights violations committed by opposition forces.
"But I have to say ... the longer the violence continues in Syria, the worse it gets, the more we are going to see hard-liners on both sides, who probably are not particular defenders of human rights, gain influence and that is a real problem, and that's why we need the transition to move more quickly," Ford said.
In his opening remarks to the panel, the Tom Lantos Human Rights Commission, Ford accused Assad of "massive" human rights violations. He said he had raised the issue continually with Assad while ambassador in Syria, starting with his first meeting with Assad 13 months ago.
"In that discussion Assad showed little interest in human rights, in fact he was rather annoyed that I raised it. And his callous disregard over the past year has degenerated into massive human rights violations that may amount to crimes against humanity."
The United States supported accountability for crimes committed by the Syrian regime, Ford said. "We are going to support the collection of evidence" on human rights violations.
The United Nations says more than 9,000 people have been killed in Syria's year-old uprising against Assad. Syria says rebels have killed some 3,000 security force members and blames the violence on "terrorist" gangs.
In addition to the charges concerning the Syrian opposition, Human Rights Watch has also accused Assad's forces of human rights abuses, including using human shields in northern Syria in their efforts to crush the rebellion.
Ford said the U.S. government did not believe that "further militarization" of the Syrian conflict was the best course and said he favored sanctions to further isolate the Syrian regime.
Washington has already frozen Syrian assets, sanctioned Syrian banks and banned imports of Syrian petroleum products. Some Republican in the U.S. Senate have suggested arming the rebels challenging Assad.
Ford said the United States wanted to talk to Arab League countries about ways to coordinate sanctions against Syria at a "Friends of Syria" conference on Sunday in Istanbul, which U.S. Secretary of State Hillary Clinton will attend.