The arrest in Yemen of a New Jersey man accused of joining al-Qaida is the latest in an alarming string of cases involving radicalized American Muslims, a trend some experts link to the duration of the wars in Iraq and Afghanistan. Yemeni authorities said this week that the American, Sharif Mobley, 26, who had worked for six years as a laborer at nuclear plants in New Jersey, had been arrested last week in Sana, the Yemeni capital, in a sweep of militants tied to the Yemeni branch of al-Qaida and the Somali Al Shabab movement. Taken to a hospital for medical treatment, Mobley allegedly grabbed a security guard's gun and shot two guards, one of them fatally, before being subdued, Yemeni officials said. The Nuclear Regulatory Commission said Friday that it was investigating Mobley's record. A spokesman for PSEG Nuclear, which operates two nuclear power plants in southern New Jersey, said Mobley had passed background checks and did routine labor and maintenance at those plants and others in Pennsylvania and Maryland from 2002 to 2008. U.S. and Yemeni officials said Mobley, like the Nigerian accused of attempting to bomb a jetliner headed to Detroit on Christmas Day, had been in contact with Anwar al-Awlaki, the Yemeni-American cleric whose radical sermons have been found on the computers of more than a dozen terror suspects in the West. Awlaki, now in hiding in Yemen, had also exchanged e-mail messages with Maj. Nidal Hasan, the Army psychiatrist accused of killing 13 at Fort Hood, Texas, in November. News of Mobley's arrest followed the disclosure of charges this week against a 46-year-old American Muslim convert from the Philadelphia suburbs who called herself 'Jihad Jane' and is accused of plotting to kill a Swedish cartoonist who had caricatured the Prophet Muhammad. The two cases are the latest in a series of terror accusations against Americans over the past year that have challenged the conventional wisdom that American Muslims are less susceptible to extremism than those in Europe. 'It's a troubling trend, fed by an ideological claim found all over the Web that says the U.S. is at war with Islam,' said Rick Nelson, director of the counterterrorism program at the Center for Strategic and International Studies in Washington and co-author of a new study of the homegrown extremist threat. The study found that the perception that the United States is targeting Muslims, fueled by years of military action in Afghanistan, Iraq, Pakistan, Yemen and other Muslim countries, plays a greater role than 'poverty or social marginalization' in turning a small number of Americans toward extremism. 