- NEW: Opposition activists: Fresh violence erupts in Douma and Hama, days after U.N. observers leave
- U.N. official: Syria says it will not accept monitors from countries aligned with 'Friends of Democratic Syria'
- Hillary Clinton: It is "absolutely deplorable" if the regime is killing residents who spoke to U.N. monitors
- At least 38 people were killed across Syria on Tuesday, opposition activists say
Are you there? Send us your images or video. Also, read this report in Arabic.
(CNN) -- U.N.-Arab League special envoy Kofi Annan expressed dismay over reports that the Syrian government resumes brutal attacks on cities once U.N. monitors leave -- the latest sign that diplomatic efforts are failing to quash the bloodshed in the country.
"I am particularly alarmed by reports that government troops entered Hama (Monday) after observers departed, firing automatic weapons and killing a significant number of people," Kofi Annan told U.N. Security Council members Tuesday. "If confirmed, this is totally unacceptable and reprehensible."
A handful of U.N. observers have visited besieged cities such as Hama, Douma and Homs -- a bastion of anti-government sentiment -- in recent days.
By Wednesday morning, violence picked up again in Douma, one opposition activist said.
"The security forces have continued their siege on Douma for the second day today," said the resident, identified only as Mohammed for safety reasons. "We desperately call on the international monitors to return to Douma to see the other face of the regime!"
Mohammed said nine people were killed in Douma on Tuesday, including the head of the Red Crescent branch in the city.
Officials with the international aid agency were not immediately available for comment on the report.
Farther north, strong explosions and gunfire rattled Hama on Wednesday, opposition activists said, three days after U.N. monitors left that city.
Annan said Syria's foreign minister told him heavy weapons and troops had been withdrawn from population centers and that military operations had ended -- in line with a six-point peace plan laid out by Annan and accepted by the Syrian regime.
Syria's deadly lies to U.N. monitors Annan described the communication as "encouraging," but added, "the only promises that count are the promises that are kept."
Shelling of Syrian city intensifies Opposition activists said escalating carnage -- including at least 38 deaths on Tuesday -- is proof that President Bashar al-Assad's regime keeps breaking its promises.
U.N. to send more monitors to Syria Annan spokesman Ahmad Fawzi corroborated that view. He said the Syrian regime claims it has pulled back heavy armor, yet "satellite imagery, however, and credible reports show that this has not fully happened."
But the government doesn't just renew attacks on cities after the observers leave -- they also reportedly target residents who spoke out to U.N. monitors.
"We have credible reports that when (monitors) leave, exchanges start again, that these people who approach the observers may be approached by security forces or Syrian army and harassed or, even worse, killed," Fawzi told the U.N. Security Council on Tuesday.
U.S. Secretary of State Hillary Clinton expressed concern over claims that the Syrian government was killing residents who speak out.
"It is absolutely deplorable if there is this kind of intimidation and harassment and possible violence against those Syrians who have every right to meet with and discuss the situation with the monitors," she said.
Clinton said U.S. officials were preparing "additional steps" in case the violence continues or if the monitors are prevented from doing their work.
The U.N. Security Council recently authorized sending up to 300 monitors for 90 days. They are tasked with observing a cease-fire that was supposed to begin April 12.
Two Chinese nationals are among the latest U.N. observers to enter Syria, China's state-run Xinhua news agency said Tuesday, bringing the number of monitors on the ground to 13.
Thirty observers are expected in the country by Monday, and 100 within a month, said U.S. Ambassador to the U.N. Susan Rice, citing comments by Herve Ladsous of U.N.'s Department of Peacekeeping Operations.
"Mr. Ladsous reported that the Syrian government has refused at least one observer based on his nationality, and that Syrian authorities have stated they will not accept (monitoring mission) staff members from any nations that are members of the 'Friends of Democratic Syria,'" Rice said Tuesday. "He underscored that from the U.N. point of view, this is entirely unacceptable."
Dozens of countries and international groups have met in "Friends of Syria" conferences in recent months to try to help stop the slaughter in Syria.
Analysis: U.N. mission does nothing to change endgame in Syria
Aside from the report that Syria is choosing which monitors it allows in, some question whether the observers will get an objective, comprehensive view of the situation.
"They are all the time watched by the security forces of the regime," said one opposition activist, who is not being identified for safety reasons.
In addition to monitoring the cease-fire, observers are also tasked with supporting the implementation of Annan's peace plan , which calls for the government and the opposition to end the violence, provide access for humanitarian groups, release detainees and start a political dialogue.
CNN cannot independently verify reports of violence and deaths within Syria, as the government has restricted access by international media.
The country has been engulfed in violence since March 2011, when the government started cracking down on demonstrators who were peacefully protesting al-Assad's regime. Opposition members say they want democratic reforms and the ouster of al-Assad, whose family has ruled Syria for 42 years.
The United Nations estimates at least 9,000 people have died since the protests began, while activist groups put the death toll at more than 11,000. Rice put the total at 10,000.
CNN's Amir Ahmed, Joe Vaccarello and Jill Dougherty contributed to this report.
