The claimed killings near the Jordanian border suggest the country is sliding into a state of permanent armed insurgency

Syrian rebels claimed to have killed 27 members of the security forces in clashes on Thursday – providing more evidence that the country is sliding into a state of permanent armed insurgency.

On the day that saw the Syrian uprising enter its 10th month, Human Rights Watch (HRW) named 74 senior officials and commanders – including President Bashar al-Assad – who it said should face investigation for crimes against humanity.

The claim that 27 soldiers and secret policemen had been killed by armed defectors in attacks on three separate roadblocks in Deraa near the Jordanian border – where the unprecedented unrest began peacefully in March in the early days of the Arab spring – was made by the British-based Syrian Observatory for Human Rights.

It was not possible to obtain independent confirmation of the report, which appears to be one of the worst attacks yet on Syrian government forces. Defectors were also said to have killed least eight soldiers on Wednesday and seven on Tuesday. Responsibility for the Deraa attacks was claimed by the Free Syrian Army.

According to the UN some 5,000 people have been killed in Syria's unrest so far.

Opposition groups reported further incidents of violence on Thursday. The Syrian Revolution General Commission had counted 12 dead by mid-afternoon, including a seven-year-old from the Khalil family in Hama.

It also named four conscripts who were gunned down in Deraa after refusing to open fire on civilians. The Local Co-ordination Committee, a network of activists, said eight had died.

Sana, Syria's official news agency, highlighted a report on the funerals of 11 "martyrs" from the army, police and security forces who had been "targeted by armed terrorist groups" while performing their duty in Homs, Hama, and Deraa.

HRW, calling for an International Criminal Court investigation of Assad and others, said Syrian army commanders had told troops to crush protests "by all means necessary," often giving explicit orders to fire on demonstrators.

Its researchers interviewed 63 army and intelligence defectors, one of whom said his brigade was told to "use as many bullets as you want" in Deraa in April.

A sniper in Homs said commanders ordered that a certain percentage of demonstrators should die. "For 5,000 protesters, for example, the target would be 15 to 20 people," he told HRW. About half of the defectors said officers who issued orders to fire at protesters also assured their men they would not be held accountable.

HRW quoted a soldier who defected from the army's 5th Division: "Our general orders were to kill, destroy stores, crush cars in the streets and arrest people."

France's foreign minister, Alain Juppé and the European Parliament called separately for Assad to step down – a demand being made with increasing frequency by western governments. Assad has denied that orders were issued "to kill or be brutal." He also claimed he was not responsible for the actions of the security forces, despite being the commander in chief.

Frederic Hof, the US state department's key official for Syria, told Congress on Wednesday that the repression may allow Assad to cling to power, but only for a short time. "Our view is that this regime is the equivalent of a dead man walking," he said.

Syria was turning into "Pyongyang in the Levant," a reference to the capital of North Korea. It was difficult to say how long Assad has left in power, he said, but added: "I do not see this regime surviving."

In Istanbul, a former ambassador-turned-dissident announced the formation of an opposition group named the National Alliance of Revolutionary Forces in Syria. Mohammad Bassam Imadi, Syria's former envoy to Sweden, said NARF would work with the larger Syrian National Council to overthrow the regime.