(CNN) -- Heavy clashes erupted across Syria on Saturday while government forces battled opposition fighters in various cities.
Here are the latest key developments in the nearly 18-month crisis:
On the ground: Shelling, ground battles rage on
At least 162 people died across Syria on Saturday, including 55 in and around Damascus, opposition activists said.
Several political activists reported that regime forces raided a hospital in the Damascus suburb of Kafar Batna, killed medical staff, and wounded patients. They said regime forces later burned the hospital.
The Local Coordination Committees of Syria, an opposition group, said the regime forces had targeted the hospital in the past because it treated protesters.
Rebel forces captured a military air force base to prevent airstrikes and shelling of civilians, a member of the opposition told CNN Saturday.
The opposition fighters laid siege to the air base for 11 days before raiding it, Ridha Al-Alwani said via Skype from the border city of Albu Kamal in Deir Ezzour province.
A Free Syrian Army spokesman confirmed taking control of the Air Defense battalion headquarters in Albu Kamal. The spokesman said the government was using the base to launch strikes against residential neighborhoods.
The military, however, still controls two other bases that it used to launch airstrikes following the rebel attack, Al-Alwani said.
In Damascus, heavy gunfire rang out as army tanks patrolled the capital, according to the opposition.
CNN cannot independently verify reports of violence, because the Syrian government limits access to international journalists.
The Syrian government: Detainees released
The Syrian government released 341 detainees on Saturday, according to the state-run Syrian Arab News Agency (SANA). It reported those released were "citizens who got involved in the recent events in the country but did not shed blood."
The detainees pledged not to repeat the acts they had committed, SANA reported.
"A number of the released stressed they will stand in support of the homeland and the exerted efforts aimed at rebuilding it and consolidating its strength," the news agency said. "They saw their release as a new start for them to go back to their normal life."
The region: Turkey wants a no-fly zone
Turkish Prime Minister Recep Tayyip Erdogan on Saturday called on the U.N. Security Council to declare a no-fly zone along the Turkey-Syria border.
"The region should be declared a no-fly zone first, and then we can take a step for a buffer zone," he told the Anatolian news agency.
He also said there are now more than 80,000 Syrians now in Turkey because of the crisis.
At the border crossing of Bab al Salam, there are now 5,000 women and children, seeking refuge. They say there is little food and water, and many people are sick.
"We won't go back until the regime is overthrown," one man at the border crossing said. "If we can't get into Turkey ... we'll be forced to take our children back under Assad's bombs," he said, referring to Syrian President Bashar al-Assad.
Diplomacy: Envoy Brahimi says the situation 'must change'
The new United Nations and Arab League envoy to Syria, Lakhdar Brahimi, said early Sunday the situation in Syria "must change" after more than a year and a half of violence.
"First, there is a call for all parties inside Syria to stop the violence. There is no doubt that this call goes first to the government," Brahimi told Al-Arabiya television.
Brahimi, who was appointed last month after previous envoy Kofi Annan stepped down, said he brings nothing new to the role "except the insistence to reach an end to the violence and start a political process that is able to realize peace and prosperity for the Syrian people."
World reaction: Russia says Syrians only must resolve the crisis
Russian Foreign Minister Sergei Lavrov said Saturday that it is unrealistic for the Syrian government to capitulate to foreign demands.
"The only possible solution on Syria is that taken by the Syrians themselves," the state-run Itar-Tass news agency reported.
"External interference should be positive: Every foreign player should make all Syrian parties, especially those on whom this player has special influence, stop violence," Lavrov said.
"But when they say the government should stop violence first and withdraw troops and military hardware from cities and then it is necessary to address the opposition, this is an absolutely nonworking scheme. This is something naive or provocative," he said, according to Itar-Tass.
Missing journalist: A call for his release
The U.S.-based Syrian Expatriates Organization, which supports Syrian activists, called Sunday for the release of American freelance journalist Austin Tice.
The 31-year-old went missing more than two weeks ago while reporting in Syria. The Washington Post, one of his employers, reported Thursday that Tice is in Syrian government custody.
The Post, Tice's family and journalist advocacy groups like the Committee to Protect Journalists have all called for his release.
"We fear for the safety of Austin Tice in Syrian government custody, where he faces inhumane conditions and possible torture. We demand his immediate and unconditional release," said Abdullah Ibraheem, a Syrian Expatriates board member.
The U.S. State Department says it is working to confirm reports of Tice's capture by the Syrian government and to obtain information about his welfare.
CNN's Hamdi Alkhshali, Yousuf Basil and Amir Ahmed contributed to this report.