By Thomas Grove and Nastassia Astrasheuskaya
MOSCOW (Reuters) - Russian Foreign Minister Sergei Lavrov said on Monday that Moscow was deeply alarmed by the killing of at least 108 people in the Syrian town of Houla but that it was clear both President Bashar al-Assad's government and rebels were to blame.
"We are dealing with a situation in which both sides evidently had a hand in the deaths of innocent people," Lavrov said after talks with British Foreign Secretary William Hague.
"Nobody is taking (blame) off the government and nobody is taking it off the fighters, but we must understand how it all happened so that such a thing never happens again," Lavrov told a joint news conference.
Lavrov hinted Moscow could increase pressure on Assad to abide by U.N.-Arab League envoy Kofi Annan's peace plan.
But he gave no indication Russia, which has aided Assad with arms supplies and U.N. Security Council vetoes and opposed external pressure for his ouster while strongly backing Annan's plan, was changing course.
Lavrov and Hague agreed foreign nations should work harder to push the government and rebels into compliance with the April 12 ceasefire but they accented different sides, with Hague suggesting Russia must lean harder on Assad.
Hague, on a pre-planned visit to Russia a day after the U.N. Security Council condemned the killing of at least 108 people in Houla, said "we look to Russia as having a particularly powerful role in being able to exert that additional pressure."
Hague said Annan's plan - whose demand for a government withdrawal of heavy weapons from cities and towns has not been fulfilled - was "at the moment the only hope for Syria to fight to break the cycle of violence."
Like Assad, Russia has blamed rebels for most of the violence that persisted since the ceasefire took effect and said foreign countries are aiding them with encouragement and weapons supplies.
Indicating Moscow is also frustrated with the government, Lavrov said it "deeply alarms us that the Annan plan is being implemented in an unsatisfactory way."
He said he and Hague agreed that "leading states ... upon which the conduct of one or the other side in Syria depend, should make additional efforts to work out clear and verifiable mechanisms for implementation of Annan's plan. We will be working on work on this in the near future."
However, Lavrov criticised nations he said were arguing that there could be no solution the crisis in Syria - where the United nations says government forces have killed more than 9,000 people since March 2011 - without Assad's exit from power.
"All the external players need to be playing the same game: the game directed at implementing the Annan plan, and not the game of the regime change," he said.
(Writing by Steve Gutterman; Editing by Alison Williams)