NEW DELHI: US defence secretary James Mattis is likely to visit India in the last week of September during which both sides are expected to discuss regional security challenges and ways to further ramp up defence ties.Issues relating to joint development of weapons system and combating terrorism in the region are likely to figure during the talks.The US defence secretary is likely to visit India in the latter part of September, official sources said.In June 2016, the US had designated India as "Major Defence Partner" intending to elevate defence trade and technology sharing with India to a level commensurate with that of its closest allies and partners.The Indo-US defence and security ties have been on an upswing and both sides are expected to discuss extensively some of the defence procurement deals during the visit of Mattis, the sources said.The situation in Afghanistan, China's growing assertiveness in the region and challenge of terrorism emanating from Pakistan are some of the other issues which may figure during talks Mattis will have with the defence minister here.On Tuesday, US President Donald Trump had vowed to boost the US' strategic partnership with India to achieve peace and stability in Afghanistan and called on New Delhi to provide more economic assistance to the war-torn country.Trump, in his first prime-time televised address to the nation as commander-in-chief, laid out his South Asia policy saying a "critical part" of it was to further develop the US' strategic partnership with India.