By Phil Stewart
KABUL (Reuters) - Insurgent attacks against Afghan and NATO forces in Afghanistan have started to decline on an annual basis for the first time in up to five years, defying predictions by intelligence analysts, General David Petraeus said on Saturday.
The number of insurgent attacks is one of the key measures used by the military to assess the success or failure of the nearly decade-old war in Afghanistan, the focus of a massive U.S. troop buildup which will start to come home this month.
Petraeus, who is due to step down as the top commander in Afghanistan in mid-July, said the number of attacks declined in May and June by "a few percent," compared to the same months in 2010. July is trending in the same direction, he said.
That compares to intelligence estimates that had predicted insurgent attacks to spike up by 18 to 30 percent this year over last Year.
"Obviously it is what we have wanted to see -- rather than the year-on-year-on-year increase that has taken place for some four or five years," Petraeus told reporters, in what was expected to be his last media briefing before he steps down.
Petraeus is due to take over as CIA director in September.
Asked whether he believed that the declining violence was a sign of the success of the "surge" of more than 30,000 forces that President Barack Obama ordered into Afghanistan in 2009, Petraeus was hesitant.
"I'm not making that pronouncement," Petraeus said. "Again, it is an important development but we need to see if it is sustained our not."
Obama is withdrawing the first 10,000 of the nearly 100,000 U.S. forces in Afghanistan this year, followed by another 23,000 by the end of next summer.
The drawdown is faster than the one that Petraeus had originally recommended but he has since voiced his support for the strategy and said he intends to carry it out.
Still, Petraeus suggested that the NATO-led coalition in Afghanistan would be able to keep up the pressure on militants, taking away their strongholds.
Usually, that process causes a spike in violence, he said, adding that although there had been no rise in overall incidents this year, the insurgents were still a dangerous enemy.
"Typically when you have a lot more friendly forces, and when you go on the offensive, violence goes up because you have to fight back," Petraeus said.
"And they're fighting back, don't get me wrong," Petraeus said, acknowledging, for example, heavy use of homemade bombs -- the number one killer of U.S. forces in Afghanistan.
(Editing by Emma Graham-Harrison)