By Mohammed Ghobari SANAA (Reuters) - The United States is closing its embassy in Yemen, the Arabian peninsula state that is a front line in Washington's war against al Qaeda, embassy employees and U.S. officials said on Tuesday. U.S. officials in Washington confirmed the embassy would close because of the unpredictable security situation in a country where a rebel group has seized control of the capital, Sanaa. State Department spokeswoman Jen Psaki declined comment. After years of crisis, Yemen now risks descending into a full-blown civil war pitting regional, political, tribal and sectarian rivals against each other in a nation that shares a long border with top global oil exporter Saudi Arabia.