Sanaa, the Yemeni capital, is once again on high alert after a French magazine released controversial cartoon depictions of the Prophet Muhammad only days after protests over an anti-Islam video.br br In an effort to boost security in the city, Washington has sent in dozens of marines to protect the US embassy.br br In a nation where drone strikes targeting al-Qaeda fighters have killed civilians, the marines' presence has caused a controversy among the political and religious leadership.br br They say it is a breach of their sovereignty. Al Jazeera's Jane Ferguson reports from Sanaa.