London, England (CNN) -- A member of al Qaeda's wing in Yemen intent on staging an attack was arrested in Britain earlier this year, the British home secretary said Wednesday.
Theresa May disclosed the development in a wide-ranging address on counter-terrorism, in which she discussed threats of violence and approaches to fighting them.
"Our police and agencies have been working to disrupt AQAP operatives in this country," she said, making reference to al Qaeda in the Arabian Peninsula.
"An AQAP associate was arrested here earlier this year. He is alleged to have been planning a terrorist attack in this country. Threats such as these are likely to continue."
Officials believe that AQAP is behind the recent plot to send bombs from Yemen to the United States. The group is based in Yemen, which has emerged as a major operating base for al Qaeda and other terror groups. May noted that "one of the devices was intercepted and made safe here."
She said in the wake of that incident, Britain ordered the suspension of air freight from Yemen and other actions, such as the "suspension of unaccompanied air freight from Somalia."
"The specifics of this attack -- notably the type of device and how it was concealed -- were new to us. The principle of the attack -- a device placed in unaccompanied baggage -- was not. It bears some resemblance to the attack on Pan Am 103 over Lockerbie in 1988."
She said last week's incident showed "beyond doubt" that "we will continue to face a threat from international terrorism for the foreseeable future."
That threat is now more diverse and more fragmented than ever before," said May, who emphasized that "public policy must respond to this changing threat."
May said that last month the government came out with a national security strategy that said terror from Northern Ireland and in the international realm "remain two of the highest risks our country faces." She pointed out that an explosive device intended to cause civilian casualties was found Saturday in a car at the Belfast airport.
"It is testimony to the success of the police and the agencies that we have not had a successful attack in this country since 2007 and there have been no casualties since 2005. But as we saw last week, the absence of an attack does not mean an absence of threat."
She says al Qaeda is weaker but still remains dangerous.
"We should neither overstate the strength and significance of al Qaeda, nor underestimate its continuing capability," she said.
May cited the dangers of Al-Shabaab, the militant group in Somalia "just across the Red Sea from Yemen."
That group "has developed links to al Qaeda and, we assess, to AQAP. It thrives in a failed state. It has aspirations beyond Somali borders."
She also mentions the North African group al Qaeda in the Maghreb, which has resorted to kidnapping.
"We do not believe the group yet has the capability to carry out a terrorist attack on British soil, but I don't doubt that would be their aspiration."
She said there has been an emergence of a "more diverse and devolved terrorist threat" that lacks a "strong, directive and commanding center and (is) joined more by ideology than hierarchy."
"The attempted attack in Times Square by the Pakistani Taliban perfectly illustrates the challenge we face," referring to a failed attempt to set off a bomb in New York's Times Square.
May cited the "new and deadly method of attack" utilized by Lashkar-e Taiba in the November 2008 Mumbai strike.
"These attacks were conducted by terrorists with assault rifles, handguns and improvised explosive devices. The attackers also used off-the-shelf technology -- satellite guidance and encrypted communications -- which you can buy across the counter anywhere in the world.
"We cannot assume that such an attack would be replicated exactly here, but we must plan for the possibility of a terrorist firearms attack in this country."
May also stressed the importance of balancing liberty and safety.
"We want to ensure that where powers are intrusive they are proportionate to the threat, necessary to reduce it to a level which we judge acceptable, and effective. These criteria -- proportionality, necessity and impact -- are vital."
She said it is important to tackle the causes of terror, such as some social and economic factors.
"We need a new approach to our engagement with Britain's Muslim communities -- one that helps to create the integrated society that we need.
"We will stop talking to Muslim communities only about counter-terrorism, and start treating them like the mature and integral parts of society that they are."
She also emphasized that success in domestic counter-terror requires "international cooperation and collaboration overseas."