ISTANBUL, Turkey (CNN) -- Syrian rebels accused government forces of bombing a hospital in the besieged city of Aleppo late Wednesday, killing at least 40 people as the conflict there ground on.
Ralib al-Omar, a leader of the Yusif al-Asma rebel group, said the attack targeted the Dar al-Shifa Hospital and that the dead included two nurses. The Local Coordination Committees of Syria, a network of opposition activists, said a doctor was among the dead as well -- one of 108 people the group said were killed across the country on Wednesday.
Dar al-Shifa is one of the main sources of medical help for people in Syria's commercial hub. In video posted by opposition activists, the blast appeared to have hit the hospital's often-crowded front lobby.
Aleppo has been the scene of some of the heaviest fighting of the 20-month-old Syrian conflict since August, and an artillery shell had hit the hospital's maternity ward earlier this year.
An estimated 37,000-plus people have been killed since protests broke out against Syrian President Bashar al-Assad in March 2011. Al-Assad responded by turning the army and police on the demonstrations, resulting in a civil war that has so far killed more than 37,000 people, according to the opposition Center for Documentation of Violations in Syria.
Most of those are civilians, though about 3,000 of the dead are government troops, the center reported last week. The government-owned Syrian Arab News Agency reported a series of clashes between security forces and armed terrorist groups -- its euphemism for opposition fighters -- and intense fighting near the Syrian-Turkish border in recent weeks has pitted loyalist Syrian forces and fighters from the rebel Free Syrian Army.
CNN cannot confirm claims by the government or the opposition because of government restrictions that prevent journalists from reporting freely within Syria.
In a sign of a potential escalation of the conflict, Turkey asked its NATO allies for Patriot missiles Wednesday to bolster its air defenses against its southern neighbor. A letter to NATO included the "formal request" that the alliance send "air defense elements," according to a Turkish government statement that cited "the threats and risks posed by the continuing crisis in Syria to our national security."
The statement added that the NATO Council would convene "shortly" to consider the matter. NATO Secretary-General Anders Fogh Rasmussen said in a Twitter post that the request would be considered without delay.
In a statement on Wednesday, Rasmussen said the letter from Turkey requested Patriot missiles that would "contribute to the de-escalation of the crisis along NATO's south-eastern border" and serve as "a concrete demonstration of alliance solidarity and resolve."
Rasmussen's statement said three NATO countries have available Patriot missiles -- Germany, the Netherlands and the United States -- and it would be up to them to decide if they can deploy them and for how long.
A NATO team will visit Turkey next week to survey possible deployment sites for the Patriot missiles, Rasmussen's statement said. Sources told CNN that Germany would be the likely source for a deployment. German Chancellor Angela Merkel said Wednesday that any decision involving her country would need the approval of Parliament.
In Turkey, Foreign Ministry spokesman Selcuk Unal said NATO forces under the command of the alliance would come to Turkey as part of the missile deployment. He noted that NATO-supplied Patriot missiles previously were deployed in Turkey in 1991 and 2003.
"It's not as if they are going to come tomorrow to be deployed," Unal said, calling the move a precautionary measure that will deter escalation along the Syrian border.
International and Turkish media reported earlier this month that Turkey planned to ask NATO to station Patriot missiles along the border with Syria, but Prime Minister Recep Tayyip Erdogan denied it at the time. Turkey has been careful to make clear it plans no offensive action and does not want a war with Syria, which shares a more than 500-mile border.
Turkish President Abdullah Gul told reporters on November 8 that while going to war with Syria was "out of the question," precautions were needed against "ballistic missiles as well as mid-range and near-range missiles."
The U.S.-made Patriot missile system -- which became well known during the first Gulf War in the early 1990s when it protected American allies against Iraqi Scud missiles -- works well against short- and medium-range missiles. Two decades later, reports about the possible deployment of Patriots have emerged as tensions steadily escalate between Syria and Turkey.
Last month, Syrian artillery shells hit the Turkish border town of Akcakale, killing five Turkish citizens. Soon after, the Turkish Parliament approved a resolution that would allow the military to carry out cross-border incursions.
Since then, Turkish forces have retaliated with artillery swiftly after more than a dozen cross-border artillery strikes believed to have been carried out by the Syrian military.
Once-cozy relations between Syria and Turkey have all but collapsed since the Syrian uprising began last year. Turkey is officially hosting more than 111,000 refugees, but the Turkish government says tens of thousands of unofficial refugees also live in Turkish cities and towns near the Syrian border.
Meanwhile, Damascus has repeatedly accused its former ally of meddling in internal Syrian affairs by funding and arming the Syrian opposition, as well as providing sanctuary and medical care to Syrian rebels.