- NEW: 17 people are killed Tuesday, including children and defectors, opposition activists say
- NEW: Turkish Airlines suspends ticket sales to Damascus and Aleppo
- Annan says the Syrian crisis cannot "drag on indefinitely"
- Syrian state-run media says it has killed members of an "armed terrorist group"
(CNN) -- Syrian authorities have banned men ages 18 to 42 from traveling abroad until they serve their compulsory military draft, a rebel army spokesman said Tuesday.
The ban "shows that the regime is preparing for the worst and they are suffering from heavy losses from our operations and the defections all across the nation," Lt. Riad Ahmed of the rebel Free Syrian Army said. "We keep asking or brothers in the armed forces to abandon the barracks and join the revolution all over Syria because it is a matter of time before the regime collapses."
President Bashar al-Assad's regime did not immediately issue a statement confirming or denying such a travel ban.
But the Syrian Revolution website posted a memo from Syrian Air saying all men ages 18 to 42 must check with the recruitment office and receive clearance before traveling.
Ahmed said Free Syrian Army operatives learned of the ban after authorities sent orders to border crossings. He said he's not deterred by the move.
"The more restrictions the Assad military will impose, the more power we will gain because this shows that the regime is in despair," he said.
At the same time, violence erupted once again across Syria, where at least 17 more people were killed Tuesday, opposition activists said.
The deaths took place all over the country, including in Homs, Idlib and Deir Ezzor, according to the opposition Syrian Network for Human Rights. The group said three children, three women and two defected military members were among those killed.
Meanwhile, U.N.-Arab League special envoy Kofi Annan arrived in Beijing on Tuesday to rally support in helping end the bloodshed in Syria.
Annan's visit to China comes after a stop in Russia, the other country that has stymied U.N. Security Council attempts to condemn the Syrian regime.
During his two-day trip to China, Annan will meet with foreign ministry officials, China's state-run Xinhua news agency said. Foreign ministry spokesman Hong Lei said China supports Annan's mediation efforts and hopes to discuss political solutions for the Syrian crisis, according to Xinhua.
Annan has offered Syria a six-point plan -- supported by the U.N. Security Council -- as a way to halt the violence.
The proposal seeks to stop the violence and the killing, give access to humanitarian agencies, release detainees, and start an inclusive political dialogue to address the legitimate aspirations and concerns of the Syrian people, according to a U.N. statement.
A spokesman for Annan said Monday that the Syrian government has formally responded to the proposals, but did not provide details. He said Annan was studying the response and would reply shortly.
Both China and Russia have said they want the violence to stop but argue that draft resolutions by Security Council peers were not evenhanded. Both countries have major trade ties with Syria, but have said they are not trying to protect a regime.
Other countries have spoken out against al-Assad's regime or severed diplomatic channels inside Syria.
A day after Turkey and Norway announced the closure of their embassies in Damascus, Turkish Airlines said Tuesday it has suspended ticket sales to Damascus and Aleppo as of April 1.
The Turkish government, which owns just under half of the company's shares, has used the airline as an extension of its foreign policy. It has extended airline routes to countries shortly after high-level diplomatic contacts and bilateral trade deals are announced. With Syria, this pairing of Turkish Airlines and government policy is working the other way around.
On Monday, the former U.N. secretary-general said the ongoing crisis in Syria cannot not be allowed to "drag on indefinitely," but resisted setting any sort of timetable.
"I think it is urgent to move ahead," Annan told reporters in Moscow. "But it is not practical to put out timetables and timelines when you haven't gotten an agreement from the parties."
But Annan said change is inevitable in Syria.
"As I have told the parties on the ground, they cannot resist the transformational winds that are blowing. They have to accept that reforms have to come, change has to come, and that is the only way to deal with the situation," he said.
So far, there has been little change in the reports of terror and violence from across Syria every day.
At least 59 people were killed on Monday as government forces shelled buildings and snipers fired on civilians, dissident groups said.
The dead include four young men gunned down in Homs when residents tried to retrieve two bodies, the opposition Syrian Network for Human Rights said.
Meanwhile, the state-run Syrian Arab News Agency said five army and law enforcement "martyrs who were targeted by armed terrorist groups" were laid to rest Monday.
SANA also said authorities killed and wounded members of an "armed terrorist group" that were trying to infiltrate Syria from Turkey.
The Syrian government routinely blames the vaguely defined "armed terrorist groups" for violence in the country, while most reports from inside Syria indicate the government is slaughtering civilians in an attempt to wipe out dissidents.
CNN cannot independently confirm reports from inside Syria because the government severely restricts access by international journalists.
While reports of carnage mounted inside Syria, foreign-based opposition members met in Turkey, aiming to form a unified front before a global conference on the Syrian crisis.
Meetings in Istanbul between exile opposition groups aim to find common ground before next week's Friends of Syria conference, which will bring representatives of many countries to Turkey on Sunday. It will be the group's second meeting.
Observers of the Syrian crisis have bemoaned a lack of unity among Syrian opposition groups as they struggle to topple President al-Assad.
"Most of the groups realize they have to unite to have a road map to get the support of the international community," said Omar Shawaf, a member of the Syrian National Council, an opposition coalition.
The opposition meetings in Istanbul come after a top military defector said armed rebel groups have aligned under the leadership of the Free Syrian Army.
U.S. Secretary of State Hillary Clinton is expected to attend the Friends of Syria conference in Istanbul, State Department spokeswoman Victoria Nuland said.
Clinton also attended the first Friends of Syria conference, held last month in Tunisia. Dozens of international leaders at the summit condemned the Syrian regime's deadly crackdown on peaceful protesters while expressing support for the Syrian opposition and the need for humanitarian aid in the country.
The United Nations estimates the Syrian conflict has killed more than 8,000 people; opposition activists put the toll at more than 10,000.
CNN's Saad Abedine, Ivan Watson, Arwa Damon and Salma Abdelaziz contributed to this report.
