NEW YORK — Evidence collected by the United States against an East African charged with providing support to a Somali terrorist organization linked to al-Qaida includes lengthy statements he made to authorities, a prosecutor told a judge Tuesday.

Assistant U.S. Attorney Christopher LaVigne made the revelation during a plea proceeding for Mohamed Ibrahim Ahmed in Manhattan. Ahmed’s lawyer, Sabrina Shroff, entered a not guilty plea on his behalf.

Ahmed, 35, a citizen of Eritrea, was brought to the United States on Saturday from Nigeria on charges that he supported al-Shabaab, a violent extremist group in Somalia.

Prosecutors say he gave the organization 3,000 euros and studied weapons and explosives at a training camp. They say he bought an AK-47 rifle, ammunition and two grenades in April in Somalia. Al-Shabaab was designated by the U.S. as a terrorist group in 2008.

LaVigne told U.S. District Judge Kevin P. Castel that evidence the government will turn over to the defense in the case includes extensive statements Ahmed made in Nigeria, along with items recovered from him.

The prosecutor said Ahmed’s statements were in six reports that amounted to 10 to 13 pages. As the prosecutor spoke, Ahmed nodded his head as he listened to a translator. The government wouldn’t disclose details on Ahmed’s statements.

His apparent cooperation with authorities seemed evident in court. At the end of the proceeding, which lasted only a few minutes, Ahmed leaped from his chair and headed toward the door leading to the cell block next to the courtroom. The marshals who accompanied him did not appear alarmed by his rapid movement.

Court papers indicated Ahmed might have been held by authorities since November, when officials say he was found in possession of documents reflecting bomb-making instructions. The indictment also said his crimes stretch from at least January 2009 through last November.

U.S. authorities would likely welcome any information Ahmed can provide about al-Shabaab.

An indictment charging Ahmed with providing material support to the organization and receiving training from the group said a former leader of al-Shabaab who trained with al-Qaida in Afghanistan prior to 2001 had called for foreign fighters to go to Somalia to join al-Shabaab in a “holy war” against the Ethiopian and African Union forces in Somalia.

The indictment said al-Shabaab’s recruitment efforts had led men from other countries including the United States to go to Somalia to engage in violent jihad — holy war.

The indictment said al-Shabaab was believed to have provided protection and safe haven for al-Qaida operatives wanted for a 2002 hotel bombing in Kenya and the 1998 bombings of the U.S. embassies in Kenya and Tanzania that resulted in 224 deaths, including 12 Americans.

It said al-Shabaab in April declared it was responsible for mortar attacks against a U.S. congressman visiting Somalia. A year before that, al-Shabaab leaders declared that their fighters would “hunt the U.S. government” and warned that the U.S. and Ethiopia should keep its citizens out of Somalia, the indictment said.

Al-Shabaab is the most active group of violent extremists targeting Somalia’s weak U.S.-backed transitional government. The indictment said it has carried out assassinations of civilians and journalists and had distributed a videotape depicting the slow decapitation of an accused spy.

Somalia, an impoverished East African nation of about 10 million people, has not had a functioning government for more than a decade.

Federal prosecutors said al-Shabaab, hoping to impose strict Islamic law throughout Somalia, has claimed responsibility for suicide bombing attacks in recent years, including five simultaneous suicide bombings targeting government, Ethiopian and United Nations facilities in October 2008.