New York (CNN) -- Six men appeared in a London court Monday charged in connection with an alleged planned terrorist bombing campaign in the United Kingdom. The six were arrested last week in Birmingham as part of what authorities called a "major operation."
All were remanded in custody during a brief hearing.
Two of the alleged cell members -- Irfan Nasser, 30, and Irfan Khalid, 26, were charged with recording martyrdom tapes and "travelling to Pakistan for training in terrorism including bomb making, weapons and poison making" sometime after Christmas Day 2010.
British authorities believe it was while they were in Pakistan that they recorded the martyrdom tapes, a source made aware of details of the investigation told CNN.
They were among four charged with preparing for an act of terrorism in the U.K. Two more were charged with failing to disclose information. One has additionally been charged with raising money for terrorists.
They were arrested September 19 in a major operation carried out by the West Midlands Counter Terrorism Unit, described by authorities as unarmed, preplanned and intelligence-led.
British police say they decided to move against the group in the early stages of their alleged attack planning before they had selected targets, as part of a new strategy to break up suspected terrorist plots as soon as authorities believe they have sufficient evidence to bring suspects to trial.
All of those arrested September 19 are from Birmingham, Britain's second-largest city, the West Midlands Police said in a news release.
So is a 20-year-old man who was arrested last Thursday and "continues to be questioned." Authorities have until this Thursday to press charges, release the man or apply for a warrant so he can be detained longer without being formally charged.
Britain did not change its terror threat level in light of the arrests, leaving it at "substantial."
The six men appeared at West London Magistrates Court Monday afternoon.
Irfan Nasser, 30; Irfan Khalid, 26; Ashik Ali, 26; and Rahin Ahmed, 25, were charged with engaging in conduct in preparation of terrorist acts, West Midlands police said.
As well as receiving terrorism training in Pakistan, Irfan Nasser and Irfan Khalid were charged with "planning a bombing campaign," "planning a suicide bombing campaign/event," "collecting money for terrorism," "advising and counseling the commission of terrorist acts by providing information about training in Pakistan," "counseling on explosives and detonators," "being concerned in the purchase of components and chemicals for a home made explosive device," "construction of a home made explosive device for terrorist acts" and "being concerned in recruiting persons for terrorist acts. "
Bahader Ali, 28, is facing two charges -- having information about acts of terrorism and entering into a funding arrangement for the purposes of terrorism. Mohammed Rizwan, 32, was charged with having information about acts of terrorism, police said.
Ashik Ali and Bahader Ali are brothers, police noted.
The alleged recording of martyrdom tapes in Pakistan was first reported by the Daily Telegraph newspaper.
British authorities continue to be concerned about U.K. militants traveling to the Afghanistan-Pakistan border region, where terrorist groups have opportunities to recruit them for operations
back home. In July a Home Office report stated that British nationals were among hundreds of Europeans training or operating in Pakistan.
British authorities have grown increasingly concerned about militants traveling to Somalia and Yemen over the last year and are still confronting high levels of homegrown violent extremism.
"In the U.K. we continue to arrest very significant numbers of people for terrorist offenses -- almost 2,000 since 9/11 but over 650 in the past two years alone. This is more than other countries in Europe," U.K. Home Secretary Theresa May said in a speech in Washington on September 16.
"Al Qaeda is now substantially weaker than it has been since 9/11," she said, "but we need to be realistic about the threats that remain."