By Andrew Gray KABUL, Jan 16 (Reuters) - U.S. Defense Secretary Robert Gates said on Tuesday insurgent attacks from Pakistan into Afghanistan were increasing, hours after Pakistan launched an air strike on a militant camp near its Afghan border, killing up to 20 people. Violence in Afghanistan surged last year to its worst since 2001. While fighting has tailed off since winter set in, big clashes have been taking place in the south and east and U.S. and NATO forces expect a fresh Taliban offensive in the spring. Thirteen Taliban were killed in clashes in the southern province of Helmand, where two British soldiers were killed in recent days, and Afghan authorities arrested an aide to Taliban leader Mullah Mohammad Omar in a town on the Pakistani border. As violence has increased in Afghanistan, pressure has mounted on Pakistan to tackle Taliban sanctuaries on its side of the lawless border, where its troops have also been battling militants. Gates, while hailing Pakistan as "an extraordinarily strong ally" of the United States in the war on terrorism, said militancy on the Pakistani side of the border would have to be dealt with. "There are more attacks coming across the border, there are al Qaeda networks operating on the Pakistan side of the border, and these are issues that we clearly will have to pursue with the Pakistani government," Gates told a news conference in Kabul. The United States has about 22,000 U.S. troops in Afghanistan. Gates said it was important to take the initiative in dealing with the security threat and if commanders in the field believed more forces were required to do that, "then I certainly would be strongly inclined to recommend that to the president". Gates flew to a remote base in the snow-clad eastern Afghan mountains on the Pakistani border to visit troops trying to stop infiltration that U.S. commanders said had surged. PAKISTANI STRIKE, ARREST Pakistan was the main backer of the Taliban before the Sept. 11 attacks but denies supporting the group since then. Hours after Gates landed in Afghanistan, a Pakistan army air strike on a militant camp near the Afghan border killed up to 20 fighters in a tribal region regarded as a hotbed of support for the Taliban and al Qaeda, Pakistani intelligence officials said. Pakistan has lost hundreds of troops fighting militants on its border and has sought political ways to isolate them, to reduce the risk of sparking a wider conflict in its tribal areas. Pakistan sealed an agreement in September with tribes in the North Waziristan area under which Pakistani troops would withdraw to garrisons on the understanding the tribes would not tolerate incursions into Afghanistan. But Lieutenant General Karl Eikenberry, the top U.S. commander in Afghanistan, told reporters that last month cross-border attacks in the area were up 200 percent on a year ago. Bomb attacks in Afghanistan jumped from 783 in 2005 to 1,677 last year and suicide attacks surged from 27 to 139, according to U.S. figures. "The safe haven that Pakistan presents cannot be over-emphasised," said a U.S. military intelligence official, speaking on condition of anonymity. "Command and control resides in Pakistan while operations occur in Afghanistan," the official said. "Training, financing, recruitment, indoctrination, regeneration and other support activities occur in Pakistan." Afghan President Hamid Karzai said the Taliban would be dealt a "serious blow" if they mounted a spring offensive. Afghan authorities arrested a Taliban spokesman and aide to the group's fugitive leader, Mullah Mohammad Omar, after getting a tip-off he would be entering the country from Pakistan, an Afghan intelligence official said. The Taliban spokesman, Mohammad Hanif, was arrested in the town of Torkham on Monday.
