ISLAMABAD (Agencies) - The top US military officer accused Pakistans intelligence agency of maintaining ties to militants in Afghanistan during a trip to Islamabad on Wednesday that was focussed on easing diplomatic tensions. Admiral Michael Mullen, Chairman of the Joint Chiefs of Staff, said Pakistans perceived foot-dragging in tackling strongholds in North Waziristan belonging to the Haqqani network and its continuing relationship with it was the most difficult part of the US-Pakistani relationship. ISI has a long-standing relationship with Haqqani network, that does not mean everybody in ISI but it is there. Its fairly well known, he said in an interview with a private TV channel. Haqqani is supporting, funding, training fighters that are killing Americans and killing coalition partners. And I have a sacred obligation to do all I can to make sure that doesnt happen. So thats at the core - its not the only thing but thats at the core that I think is the most difficult part of the relationship, Mullen said. I dont know what kind of relationship hes talking about, a senior Pakistani intelligence official told Reuters. If he means were providing them with protection, with help, thats not correct. Even if you are enemies, you have a relationship. He said Pakistan had attacked Haqqanis positions in the past. Right now, we are not attacking him because we are fully engaged against another group, the Tehreek-e-Taliban Pakistan (TTP), he said. Talking to another TV channel, Mullen said the Pak-US ties are facing strains for the last few months and issues between the two countries are very much complicated. He confessed a rapid solution to these issues was not possible. However, he hoped that the issues would be resolved with the passage of time. To a query, Mullen confessed drone attacks are not coming up with positive impact. Terrorism is still spreading in the region and no instant solution is possible, he added. He said Prime Minister Yousuf Raza Gilanis recent trip to Kabul is a positive development. US wants a peaceful and political solution to Afghanistan and we are pondering over a reconciliation process with Afghan groups, he said. He further said the US would start troop pullout from Afghanistan in July this year and We have no intention of establishing permanent military bases in Afghanistan. However, US will remain there to train Afghan troops, he said. Meanwhile, talking to reporters at US Embassy, Mullen said leaders in both Pakistan and the United States recognise the importance of a strategic partnership with each other and will work through problems to ensure it remains strong. He acknowledged relations between the two countries hit a rough patch after CIA contractor Raymond Davis shot dead two men in Lahore. When we go through a crisis like this, the focus is to assess where we are, [determine whether there are] causal factors with respect to that, and assess that and move forward, Mullen told reporters. Relations between the two militaries remain good, the Chairman said. We are experiencing better coordination in the [Afghanistan-Pakistan] border area than weve ever had, he said. I have more relationships up and down the chain of command in ways a couple of years ago just didnt exist - all of which Im encouraged by. The growth of relations is not limited to the Pakistani army. The Pakistani air force and navy are partnering with the US Air Force and Navy, the Chairman said. Overall, Im optimistic, but fully aware and fully cognizant of the very difficult time weve recently been through, he said. Mullen said he is concerned about the growth and threat of terrorism in Pakistan, noting that the Lashkar-e-Taiba is not just an eastern Pakistan threat focused on India. I see them with global aspirations, he said. Several terrorist organisations - including the Haqqani network, al-Qaeda, LeT and the Jamaat-ud-Dawaa - are working together, the Chairman added. Theres a syndication thats occurring in the region over the course of the last three years that is more and more worrisome, he said. And the Tehrik-e-Taliban, which Pakistani government officials see as the main threat to the country, has espoused aspirations outside the region, Mullen added. The syndication means that terrorist leaders merge their capabilities and assist each other in attacks, the Chairman explained. Thats what leads me to believe that the border area between Afghanistan and Pakistan is the epicentre of terrorism in the world, he said. And it breeds more and more of capability over time. All countries in the region need to be involved, Mullen said, and that includes India. Its going to get worse over time, and they will kill more and more innocent people over time, he said. Responsible civilian leadership in all these countries has to continue to address these issues. The US Joint Chiefs of Staff also called on Chairman Joint Chiefs of Staff Committee General Khalid Shameem Wynne. According to sources, both discussed a host of issues like war against terrorism, cooperation to expand Pak-US military ties, Afghanistan situation and overall security in the country. Military sources divulged that CJCSC Gen Wynne raised the issue of drone attacks with Mullen, saying the strikes are against the sovereignty of Pakistan. Mullen said currently relations between Pakistan and US are passing through a difficult phase, but both the countries are looking to establish strong ties. He said tense relations between the two countries would be dangerous for the entire region, sources said. Mullen has arrived in Pakistan for talks on security issues, focusing on the anti-terror war and how to ease tension between the two allies. A US embassy statement issued after the admirals talks with Kayani and Pakistani Chairman of Joint Chiefs of Staff Committee General Khalid Shameem Wynne, said Mullen had promised Pakistan continued support in its fight against militancy. Throughout the visit, the admiral emphasised the long-term US commitment to supporting Pakistan in its fight against violent extremists, the statement said. Pakistans Foreign Secretary Salman Bashir left for the United States on Tuesday for two-day talks with State Department officials aimed at bringing back on track bilateral dialogue, a senior government official told AFP.