Describing as an "important breakthrough" the arrest of two persons by FBI for plotting terror attacks against India, US Ambassador Timothy J Roemer on Wednesday said radical extremists planning attacks are a common threat demanding a shared solution, close cooperation and bold resolve.

However, the Ambassador refused to divulge the details of the case saying, "We cannot comment on the ongoing investigations and judicial proceedings."

"We congratulate our law enforcement agencies on this important breakthrough in the fight against terror that challenges both the United States and India," he said, according to a US embassy release here.

Roemer said both US and India stand committed to bringing terrorists to justice and will press forward aggressively until this goal is accomplished. According to the US investigating authorities, Pakistan-based terror group Lashkar-e-Taiba was planning to use an American national to carry out a major terrorist attack in India.

The man, identified as David Coleman Headley, was arrested early this month by FBI's Joint Terrorism Task Force at O'Hare International Airport before boarding a flight to Philadelphia, intending to travel to Pakistan. 49-year-old Headley, along with a Canadian citizen of Pakistani origin, has been arrested on charges of plotting a terror attack.