WASHINGTON — Government forces fired at least six short-range ballistic missiles at rebel groups in northern Syria in the past several days, according to U.S. officials, a potentially significant escalation of a civil war that has killed more than 40,000 people.

U.S. officials and the group Human Rights Watch also alleged Wednesday that Syrian government forces are dropping incendiary devices similar to napalm weapons in populated areas.

The officials described the tactics as acts of desperation as rebels gain momentum in the nearly two-year fight to oust President Bashar Assad.

“How desperate do you need to be to launch a ballistic missile against your own people in your own country?” a senior Obama administration official said. “It’s the last tool you would use in a counterinsurgency” because of the risk of civilian casualties, particularly in a conflict in which most of the fighting has occurred in urban areas.

A NATO official in Brussels told Reuters that there were indications “they were Scud-type missiles.”

The bulk of Syria’s substantial missile arsenal consists of Russian- and North Korean-made Scuds, which have a range of up to 300 miles. Scuds, most infamously used by the Iraqi government of Saddam Hussein during the 1991 Persian Gulf War, are notoriously inaccurate, although modifications since then are said to have improved their capabilities. In the 1991 war, 28 U.S. troops were killed when a Scud hit their barracks in Dhahran, Saudi Arabia.

U.S.-made Patriot missiles were effectively used against Scuds in the Gulf War, and NATO has agreed to deploy Patriot batteries in Turkey, which shares a 550-mile-long border with Syria.

As fighting continued in the suburbs of Damascus, the Syrian Interior Ministry said three bombs, at least one of them in a car, had collapsed walls of the ministry building and killed at least five people. The bombs have been a trademark of extremist groups that Western governments say are increasingly infiltrating the insurgency.

On Tuesday, the Obama administration designated one of the groups, the Al-Nusra Front, also known as Jabhat Al-Nusra, as a global terrorist organization. The administration says Al-Nusra is part of the al-Qaida organization in neighboring Iraq.

Meanwhile, more than 100 governments, including the U.S., attending a Friends of Syria meeting in Marrakech, Morocco, officially recognized the recently formed Syrian Opposition Coalition as “the legitimate representative of the Syrian people and the umbrella organization under which the Syrian opposition are gathering.”

The recognition came barely a month after the coalition was organized to represent Syrians outside and within the country, where the opposition has failed to dislodge Assad’s core support among minority groups, including his Alawite sect, an offshoot of Shiite Islam. Many Alawites, along with Christians and other minorities, fear a takeover by the rebels, who are largely Sunni Muslims.

A U.S. official who attended the Morocco meeting praised the coalition’s president, Mouaz al-Khatib, an Islamic cleric considered a moderate. Khatib indirectly criticized the Obama administration’s terrorist designation for the Al-Nusra Front, asking for reconsideration of what he described as an unnecessary attempt to divide anti-Assad forces.