Updated

The chairman of the Senate Homeland Security Committee is urging Google to take further action against extremist content online after police in New York City arrested a man who was allegedly plotting a terrorist attack with help from the Internet.

27-year-old Jose Pimentel of Manhattan, described by New York City Mayor Michael Bloomberg as an "al Qaeda sympathizer," was arrested Saturday on state terrorism-related charges, accused of trying to build bombs targeting police and post offices in New York City and U.S. troops returning home.

In a letter Tuesday to Google Chief Executive Officer Larry Page, Sen. Joe Lieberman, I-Conn., expressed concern that Pimentel was able to "share his support for violent Islamist extremism" and spread his "hate-filled writings" through the a website hosted by Google.

"As demonstrated by this recent case, Google's webhosting site Blogger is being used by violent Islamist extremists to broadcast terrorist content," Lieberman told Page in the letter, obtained by Fox News. "Pimentel's site is just one of the many examples of homegrown terrorists using Google-hosted sites to propagate their violent ideology."

At one point, according to Lieberman, citing charging documents filed in the case, Pimentel posted a message online saying, "People have to understand that America and its allies are all legitimate targets in warfare," including "all kinds of buildings where money is being made to help fund" the wars in Iraq and Afghanistan."

Lieberman said in his letter that Google agreed in 2008 to "expressly ban terrorist content" on YouTube, and a year ago introduced a "flag" button on YouTube.

"I continue to appreciate and commend these important first steps, but I am disappointed that Google has not developed a consistent standard throughout its many platforms," Lieberman wrote, adding that Blogger "does not expressly ban terrorist content nor does it provide a 'flag' feature for such content."

While the private sector "plays an important role in protecting our homeland," Google's "inconsistent standards are adversely affecting our ability to counter violent Islamist extremism online," Lieberman said.

A Google representative told Fox News that the issues raised by Lieberman are taken seriously, and already addressed.

"Blogger's content policies prohibit, among other things, dangerous and illegal activities, threats of
violence, and encouraging others to take violent action against another person or group of people," the representative said.

An early-morning email to Google seeking comment was not immediately returned.

At a press conference Sunday announcing Pimentel's arrest, New York City Police Commissioner Raymond Kelly said Pimentel had been planning for months to build a bomb, but he "clearly jacked up his speed" after a September drone strike in Yemen killed Anwar al-Awlaki, the U.S.-born cleric who had become a leader of al Qaeda in the Arabian Peninsula -- or AQAP.

Bloomberg said Sunday that Pimentel represents the "lone wolf" type of threat FBI Director Robert Mueller has warned about as U.S. forces erode the ability of terrorist groups to carry out large-scale attacks.

At a Senate Homeland Security Committee hearing in September, Mueller and National Counterterrorism Center director Matt Olsen warned of AQAP's "propaganda efforts" online, including a polished magazine called "Inspire" that seeks to radicalize Westerners and has offered step-by-step bomb-making instructions.

Pimentel allegedly used "Inspire" to help build his bomb targeting New York City.

"One of the biggest concerns about the nature of the information is it's quite basic," Olsen said at the hearing in September. "It doesn't require someone to be particularly sophisticated to follow those instructions."

Mueller said that while authorities have tools to address such content online, "The fact of the matter is that once you upload something (to the Internet) … it is exceptionally difficult to try to eradicate it."

"In fact, I would say impossible," Mueller added.

-- The Associated Press contributed to this report.