US President Barack Obama fired McChrystal, his top military commander in Afghanistan, on Wednesday for remarks he and his aides made in an explosive magazine article that disparaged the president and other civilian leaders.

Obama named General David Petraeus, widely credited with salvaging the war in Iraq, to replace McChrystal.

Maj. Gen. Richard Mills, a US Marine Corps officer in command of NATO forces in southwestern Afghanistan, said Petraeus may review some policies; but he was not sure the shakeup would lead to any change in the rules of engagement governing the use of force by soldiers in Afghanistan.

"I think our rules of engagement are flexible enough that we are able to give the troops what they need," Mills told reporters in London via video link from the southern Afghan province of Helmand.

"I don't believe necessarily that the change that took place at headquarters ... will have direct impact on the street here in Helmand — possibly never, certainly not for a while," he said.

International forces have inflicted fewer Afghan civilian casualties due to more stringent rules of engagement, the coalition says. Winning over civilians while reinforcing military sweeps of insurgent-held areas is a centerpiece of the strategy devised by McChrystal.

However, as NATO casualties mount, some soldiers chafe at rules on use of force that they see as too restrictive.

The Rolling Stone article that brought down McChrystal quoted some US soldiers protesting angrily about the rules.

Obama said on Thursday his removal of McChrystal would not disrupt strategy in Afghanistan. The war has reached a critical stage despite the presence of about 140,000 foreign troops, with the Taleban at its strongest since the Islamist movement was overthrown in 2001 by the US-led invasion.

June has already been the deadliest month for foreign forces, with 79 troops killed.

Mills, who commands some 9,500 British troops as well as US soldiers fighting in Helmand, said US Marines had replaced a company of British Royal Marines stationed near the Kajaki dam in northern Helmand province.

That has freed up 150 Royal Marines to reinforce the British force at nearby Sangin, where many of the 307 British soldiers killed in Afghanistan since 2001 have died, including at least three this week.

"Sangin is difficult ground. It is key terrain to the insurgents. It is one of the last of the population centers that they contest and they are giving it up very reluctantly, but they are giving it up," Mills said.