Washington: Visiting Afghan President Ashraf Ghani has warned that extremist groups such as Islamic State (IS) pose a "grave and present danger" to Afghanistan's security transition.

"Afghanistan's security transition took place against the backdrop of the unexpected rise of religious extremism in the Middle East," Ghani on Wednesday told a joint session of US Congress. " Terrorist movements whose goal is to destabilise every state in the region are looking for new bases of operation. We are the front line, Xinhua reported".

Just hours before Ghani's speech to US lawmakers, at least six people were killed and more than 30 were wounded in a suicide car bombing near the presidential palace in Kabul, the Afghan capital city. "From the West, the Daesh is already sending advance guards to southern and western Afghanistan to push our vulnerabilities," said Ghani, referring to IS in its Arabic name.

"To the south, Pakistan's counterinsurgency operations ... are pushing the Taliban from South Waziristan towards Afghanistan's border regions. " Ghani was currently on a week-long state visit to the US to lay the groundwork for new relations between the two countries after more than a decade of troubled ties under the leadership of former Afghan President Hamid Karzai.

Given the deficiencies in the Afghan security forces which now stood at about 330,000, a fragile new government which failed to form a full-member cabinet six months into formation, and fear that IS would gain a foothold in Afghanistan, US President Barack Obama announced Tuesday that no reduction of US troops in Afghanistan would occur this year.

Obama had previously planed to reduce the current level of 9, 800 US troops in Afghanistan to around 5,500 by the end of 2015 and withdraw all troops by the end of 2016 when Obama's presidency comes to an end. Meanwhile, Obama said drawdown timeline through 2016 would be decided later this year.

"The specific trajectory of the 2016 drawdown will be established later this year to enable our final consolidation to a Kabul-based embassy presence by the end of 2016," said Obama. The White House spokesperson Josh Earnest on Monday left open the possibility of leaving about 1,000 to 1,500 troops in Afghanistan for protection purpose.

"The President does envision a scenario where the US military presence in Afghanistan by early 2017 reflects the need to protect the substantial diplomatic presence that the US will maintain in Afghanistan," Earnest told reporters in the daily briefing.