* Opposition Shi'ite preacher accused of "inciting hatred"
* Authorities free him after questioning, impose travel ban (Adds release of Sheikh after questioning, quotes from sermon)
MANAMA, Dec 28 (Reuters) - Bahraini authorities detained the head of the main Shi'ite opposition group on Saturday for questioning over comments he made in a religious sermon but later freed him, his group said.
Sheikh Ali Salman's al-Wefaq Islamic Association said after his release that he would be subject to a travel ban preventing him from leaving Bahrain.
Bahrain's interior ministry said earlier in a Twitter message that Sheikh Salman had "incited hatred" of the government and "promoted rioting and vandalism".
The questioning came nearly two months after the tiny Gulf kingdom, which is ruled by the Sunni Muslim Al-Khalifa dynasty, charged Sheikh Salman with insulting the interior ministry.
He was the most senior opposition figure to have been charged since majority Shi'ites began protests in 2011 to demand political reform and a greater role in running the country.
In his Friday sermon, Sheikh Salman urged his followers to react peacefully to what he described as "state violence".
"Repression cannot stop a stirred people," he said, according to the text of the sermon seen by Reuters.
"Now they have doubled the number of arrested people. We don't want one more person arrested but we are ready to have 10,000 prisoners, including ourselves, and 20,000. We will not surrender," he said.
In a message to supporters on Saturday evening confirming his release, Sheikh Salman again urged them to stay peaceful.
TWO SIDES FAR APART
Wefaq said Sheikh Salman had first been summoned for questioning by the Criminal Investigations Department and then transferred to the Public Prosecution Office.
Bahraini authorities have recently summoned a number of political activists and rights campaigners for questioning over statements which they say incite violence.
Wefaq's deputy leader, Khalil al-Marzouq, was arrested in September and is on trial for inciting terrorism.
Wefaq and the government launched talks in February aimed at ending the Shi'ite protests, but they have failed to end the political crisis, with the two sides apparently far apart on the opposition's main demand for an elected government.
Wefaq wants a constitutional monarchy with a government chosen from within a democratically elected parliament.
The U.S. Fifth Fleet, which guards strategic oil shipping routes, is based in Bahrain, a key regional ally of the West.
Brian Dooley of U.S.-based Human Rights First said the questioning of Sheikh Salman was an attempt by Bahrain to muzzle dissent.
"In targeting the leaders of peaceful opposition, the security forces are making an already volatile situation even more unstable," he said in an emailed statement. (Reporting by Farishta Manama Saeed and Rania El Gamal in Dubai; Writing by Mahmoud Habboush; Editing by Gareth Jones)