DETROIT, Michigan (AFP) – A Nigerian man who tried to blow up a Detroit-bound plane on Christmas Day has confessed to training with an Al-Qaeda bombmaker in Yemen, security officials told the US media on Saturday.

The allegations highlight Yemen’s growing centrality in global terror plots as the country’s government carries out an offensive against Al-Qaeda suspects, that has reportedly killed 68 alleged militants in the past 10 days.

New details emerging about Umar Farouk Abdulmutallab suggested his abortive attack on Northwest Airlines Flight 253 was planned in Yemen by Al-Qaeda members who even sewed an explosive device into the 23-year-old’s underwear.

Law enforcement officials told US media that Abdulmutallab had offered several details about his links to Al-Qaeda and his plan to take down the flight en route from Amsterdam.

Abdulmutallab told investigators that a radical Yemeni cleric he contacted through the Internet put him in touch with an Al-Qaeda leader living in Yemen, ABC News said.

He described spending a month at an Al-Qaeda compound north of Yemen’s capital Sanaa and said he was denied permission to leave the site until he completed his training alongside a Saudi Al-Qaeda bombmaker.

US counterterrorism officials said the Nigerian claimed he received specific instructions about how to carry out the attack, NBC News said.

He claimed he was told to blow up the plane as it approached Detroit because it would produce more casualties and collateral damage on the ground if it crashed into a densely populated area.

Details emerging from Abdulmutallab’s homeland suggested the young man had been a religious teenager who became radical after studying at University College London.

Nigeria’s This Day newspaper reported that he relocated to Egypt and then Dubai, and while in the United Arab Emirates told his family that he was severing all contact with them.

His attitude worried his father so much that he informed the US embassy in Abuja about his son’s activities.

But Dutch authorities said Abdulmutallab had a valid US visa when he passed through Amsterdam and his name was reviewed by US authorities before he boarded the Airbus 330 travelling from the Netherlands to the Michigan city of Detroit.

Details about when Abdulmutallab may have travelled to Yemen were still unclear, but charges filed against the Nigerian on Saturday revealed new information about the device he tried to detonate.

The US Justice Department alleged in charging documents that he went to the bathroom before the plane began its final descent, spending 20 minutes away from his seat before returning and saying he had an upset stomach.

“He pulled a blanket over himself. Passengers then heard popping noises similar to firecrackers, smelled an odor and observed Abdulmutallab’s pants leg and the wall of the airplane on fire,” the affidavit said.

“One flight attendant… stated that she asked Abdulmutallab what he had had in his pocket and he replied ‘explosive device.’

“A passenger stated that he observed Abdulmutallab holding what appeared to be a partially melted syringe, which was smoking. The passenger took the syringe from Abdulmutallab, shook it to stop it from smoking and threw it to the floor of the aircraft,” the affidavit added.

Remnants of the syringe had been recovered and were believed to be part of the explosive device, the document said.

The affidavit described the device as containing PETN, also known as pentaerythritol, “a high explosive” that is similar to nitro-glycerin.

The two apparent components of the device, the syringe and the explosive material were sewn into Abdulmutallab’s underwear by Al-Qaeda operatives in Yemen, ABC News reported, citing federal authorities.

Bernard Haykel, a US expert on the Arabian peninsula at Princeton University, told AFP that Yemen has longstanding ties to Al-Qaeda.

“Yemen has always been very important for Al-Qaeda. They always had a lot of recruits from Yemen, going back to the 1980s, when many Yemenis have gone to fight the Soviets in Afghanistan. It’s a very old connection,” he said.

He added that after the defeat of Al-Qaeda in Saudi Arabia, “many of the Saudis who survived the Saudi government attacks on them regrouped in Yemen.

The country has come under US scrutiny in recent months, particularly in the wake of the Fort Hoods shootings in Texas, which killed 13 people.

The man accused of perpetrating that attack, Nidal Hasan, was linked to Yemeni cleric Anwar al-Aulaqi, who has encouraged US Muslims to carry out militant attacks and praised the Fort Hood massacre.