San'a, Yemen - In its strongest language yet, Yemen's government declared Thursday that there are limits to its military cooperation with the United States, warning that any direct U.S. action in this impoverished Middle East nation could bolster the popularity of Islamic militants.

"If there is direct intervention by the United States, it will strengthen al-Qaida," warned Rashad al-Alimi, Yemen's deputy prime minister for security and defense. "We cannot accept any foreign troops on Yemeni territory."

The statement underscored the rising concern among Yemen's leadership of a domestic backlash that could politically weaken the government and foment more instability. In recent days, top Yemeni officials have publicly downplayed their growing ties to Washington, fearing they will be perceived by their opponents as weak and beholden to the United States.

Alimi, speaking at a crowded press conference Thursday, also said that Umar Farouk Abdulmutallab, the 23-year-old Nigerian suspect who allegedly tried to bomb an American airliner on Christmas Day, had likely met with Yemeni American cleric Anwar al-Aulaqi. Aulaqi is also linked to Nidal Malik Hasan, a U.S. Army major who is charged with killing 13 people in a shooting spree at Fort Hood, Tex., on Nov 5.

Discussing Abdulmutallab's stay last year in Yemen, Alimi echoed an account he gave The Washington Post in an interview last week. He said Abdulmutallab had traveled to Shabwa province, where he likely met with al-Qaida operatives in a house owned by Aulaqi.

Abdulmutallab arrived in Yemen in August, ostensibly to study at an Arabic-language school in the capital, San'a. School officials said he left the school in late September, clutching an exit visa. But authorities believe that instead of leaving Yemen, he traveled to Shabwa. The young Nigerian left Yemen on Dec. 4, Alimi said.

U.S. investigators believe the airplane-bombing plot originated in Yemen and that Abdulmutallab received chemical explosives and training during his stay in the country.

But Alimi asserted Thursday that Abdulmutallab had received the chemical explosives for the failed attack from Nigeria.

It was unclear how the engineering graduate could have received explosives there: flight records show he spent four hours in the Lagos airport on Dec. 24 before boarding a KLM flight to Amsterdam. He then boarded Northwest Airlines Flight 253 bound for Detroit.

When asked what proof he had that the explosives came from Nigeria, Alimi replied: "That question should be directed at the Nigerian authorities and the Dutch government. It's not related to the Yemeni security apparatus."

In an extensive accounting of a Dec. 17 U.S.-backed operation, the government said its security forces "had seized a group of terrorists" in possession of the same explosives used in an attempted assassination of Saudi Prince Mohammed bin Nayef in August, according to a report published by the state-run Saba news agency this week.

Investigators believe that such explosives were also used in the attempted airliner bombing, in which Abdulmutallab is charged with trying to detonate chemical powders that were sewn into his underwear.

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The incident has cast an unwanted spotlight on Yemen, already beset by multiple problems including a civil war, a simmering secessionist movement, high poverty and unemployment and declining oil revenues. Alimi has blamed U.S. authorities for failing to share intelligence that he said could have helped Yemen pick up Abdulmutallab before he left Yemen.

Yemeni security forces, Alimi said, have tracked down a number of Al-Qaida operatives who had contact with Abdulmutallab, but he declined to identify them.

"We are pursing many of many of these elements that are connected to this subject," he said. "Some of these elements have been killed; others have been arrested and are being investigated. We will announce the results of these investigations later."

Alimi also said he believed that Al-Qaida had first recruited Abdulmutallab in Britain. The Nigerian lived in London from 2005 to 2008.

U.S.-backed Yemeni forces launched an air strike Dec. 24 that targeted a gathering of suspected Al-Qaida leaders. U.S. and Yemeni investigators believe the gathering included Al-Qaida in the Arabian Peninsula leader Nasser al-Wuhayshi; his deputy Said Ali al-Shihri and Aulaqi. U.S. and Yemeni officials now say that Aulaqi is alive, but they cannot confirm the fates of the two Al-Qaida leaders.

Mohammed Ahmed Saleh Omair, a mid-level Al-Qaida leader who Yemeni authorities say was killed in the strike, had also met with Abdulmutallab, Alimi said.