The strikes killed at least 152 civilians this week.
According to a network of local Syrian activists, air strikes have killed more than 4300 civilians across Syria since July 2012.
"In village after village, we found a civilian population terrified by their country's own air force," said Ole Solvang, an emergencies researcher for the organisation. "These illegal air strikes killed and injured many civilians and sowed a path of destruction, fear and displacement."
The report said government forces deliberately targeted four bakeries, where civilians were waiting in breadlines, eight times and hit other bakeries with artillery attacks. Repeated aerial attacks on two hospitals suggest that the government also deliberately targeted these facilities.
In addition to the attacks on the bakeries and hospitals, Human Rights Watch said 44 other air strikes were unlawful under the laws of war. Syrian forces used means and methods of warfare, such as unguided bombs dropped by high-flying helicopters, which under the circumstances could not distinguish between civilians and combatants and thus were indiscriminate.
Human Rights Watch said the government's use of unlawful means of attack has also included cluster munitions, weapons that have been banned by most nations because of their indiscriminate nature. Human Rights Watch has documented government use of more than 150 cluster bombs in 119 locations since October 2012.
Reuters reported that more than 70 000 people have been killed in the conflict, which started with peaceful protests that were violently suppressed. The protests were against four decades of Assad family rule.
Stepped up
More than a million Syrians have fled abroad and millions have been displaced inside the country.
Meanwhile, John Kerry the United States secretary of state, said this week that the Obama administration was weighing "stepped up" efforts to support the rebel fighters and that such proposals had been "front and centre" in administration discussions over the past week.
Western and Middle Eastern nations trying to help the Syrian opposition in its civil war against President Bashar al-Assad, were scheduled to meet in Turkey on April20, a US official said this week.
Kerry will attend the gathering of the so-called Friends of Syria "core group" in Istanbul, said the official, who spoke to Reuters reporters in London on condition of anonymity.
The radicalisation of elements of the divided opposition has tempered the enthusiasm of some Western nations for supporting the rebels militarily. Iraq's al-Qaeda wing said this week it had united with Syria's al-Nusra Front, a kindred group.
Michael Stephens, a Doha-based analyst for the Royal United Services Institute, a security think-tank, said the presence of Syrian National Coalition leaders at a meeting of the G8 this week was designed to help the coalition to shore up its international legitimacy after the Arab League recognised it as the sole representative for Syria.
"It shows there's a graduated process, where they went from laughing stock to being approved by the Arab League to being listened to by G8 leaders," he said.
"There's a groundswell of support that appears to be building up behind them," the UK's Guardian newspaper quoted him as saying.