By Louis Charbonneau and Michelle Nichols
UNITED NATIONS (Reuters) - The size and sophistication of some recent bomb attacks in Syria suggest that "established terrorist groups" may have been behind them, the U.N. chief said on Friday, in a letter in which he urged states not to supply arms to government or rebel forces.
"The overall situation in Syria remains extremely serious and there has been only small progress on some issues," U.N. Secretary-General Ban Ki-moon told the Security Council in the letter on the 14-month-old conflict between government forces and increasingly militarized opposition.
"There is a continuing crisis on the ground, characterized by regular violence, deteriorating humanitarian conditions, human rights violations and continued political confrontation," he said in the letter, which was obtained by Reuters.
The U.N. Security Council will discuss Ban's progress report and hear a briefing from international mediator Kofi Annan on Wednesday about the situation in Syria. Annan will visit Syria soon to discuss the lack of significant progress in implementing his six-point peace plan.
Earlier this year, Annan brokered a six-point peace plan, which called for an end to violence by all sides, withdrawal of troops and heavy weapons from cities, deployment of the monitoring force, and dialogue between the government and opposition aimed at a Syrian-led "political transition."
Ban's letter will likely confirm the views of the United States and its allies that the Annan plan is not bringing peace to Syria, largely due to the failure of Syrian President Bashar al-Assad's government to comply with its terms and the increased militarization of the opposition.
Ban said the unarmed U.N. observer force in Syria (UNSMIS), which is being deployed to monitor a cease-fire plan that has yet to take hold, noted that "significant parts of some cities appear to be under the de facto control of opposition elements.
"There is an overall atmosphere of tension, mistrust and fear," Ban said. "The overall level of violence in the country remains quite high."
"The Syrian army has not ceased the use of, or pulled back, their heavy weapons in many areas," he said. "On several occasions, UNSMIS has heard the sound, or seen evidence, of shelling in population centers."
Ban's report to the council was his latest 15-day progress report as required under a resolution the 15-nation council adopted last month to establish a 300-member unarmed observer force for Syria. Ban said the force would likely be fully deployed by the end of the month.
Ban said there has been an increase in the number of bombings in Syria, above all in Damascus, Hama, Aleppo, Idlib and Deir al-Zor.
"The sophistication and size of the bombs point to a high level of expertise, which may indicate the involvement of established terrorist groups," he said, without specifying to which groups he was referring.
'MASSIVE' HUMAN RIGHTS VIOLATIONS
Ban has said he believes al Qaeda was responsible for two suicide car bombs that killed at least 55 people in Syria this month and that the death toll in the country's 14-month conflict was now at least 10,000, though U.N. officials say they lack hard evidence to prove the al Qaeda link.
Syria has maintained all along that it is facing a "terrorist" conspiracy funded and directed from abroad, not least by resource-rich Gulf monarchies Saudi Arabia and Qatar, which have called for arming the fighters aiming to oust Assad.
Ban also warned countries against providing either side with military aid.
"Those who may contemplate supporting any side with weapons, military training or other military assistance, must reconsider such options to enable a sustained cessation of violence," he said.
"The government reportedly continues to receive military equipment and ammunition from other countries, and there are also reports of weapons being sent to opposition forces," Ban said.
A Russian cargo ship loaded with weapons is en route to Syria and due to arrive at a Syrian port this weekend, Al Arabiya television said in a report that Western diplomats in New York described on Friday as credible.
Ban referred to reports of a "stepped-up security crackdown by the authorities that has led to massive violations of human rights by government forces and pro-government militias, including arbitrary arrests, torture, enforced disappearance and summary execution of activists, opponents and defectors."
He also cited reports of human rights abuses by the opposition, albeit "on a lesser scale, but including instances of arbitrary detentions and summary executions of government forces and other pro-government elements."
(Editing by Stacey Joyce)