US Defense Secretary Robert Gates on Thursday said Pakistan's failure to put pressure on Taliban forces on the country's border with Afghanistan had fueled a rise in violence, but said Islamabad appeared to recognize the problem. A 40 percent spike in violence in east Afghanistan in the first five months of 2008 "is a matter of concern, of real concern, and I think that one of the reasons that we're seeing the increase ... is more people coming across the border from the frontier area," Gates told a news conference. He said "the ability of the Taliban and other insurgents to cross that border and not being under any pressure from the Pakistani side of the border is clearly a concern."