By Khaled Yacoub Oweis
DAMASCUS (Reuters) - Security forces wielding batons dispersed 150 demonstrators who had gathered in central of Damascus on Wednesday in the most serious protest against Syria's ruling hierarchy since revolts spread in the Arab world.
Scores of plainclothes security officers charged the demonstrators assembled outside the Interior Ministry to demand the release of political prisoners, a Reuters witness said.
One demonstrator suffered a gash on his head, others were beaten and at least 15 were detained, including leading political activist Suhair al-Attasi.
Attasi had said Syrian authorities would not be able to escape the tumult shaking the Arab world by refusing to open the country's political system and allowing free expression.
"They pulled Suhair by her hair and took her away," one demonstrator said.
Among those arrested were Tayyib Tizini, 69, a professor of philosophy at Damascus University, and the sister and son of Kamal Labwani, a doctor jailed for "weakening national morale" and "inciting a foreign country to invade Syria."
The gathering in Marjeh square, an Ottoman-era square in the center of the capital, had been silent, with protesters raising pictures of imprisoned relatives and friends, before security forces started hitting them with their batons.
One of the demonstrators carried a picture of Mohannad al-Hassani, a lawyer who won an international human rights prize last May for representing political prisoners. He was sentenced a month later to three years in jail.
"This is chaos," a security officer shouted at protesters. "No this is a peaceful protest," a demonstrator answered.
The protesters dispersed after the attack, and security forces continued arresting more people, shoving them into a bus and a darkened van. An interior ministry official said "infiltrators" had tried to stir chaos in front of the ministry.
A brief counter-demonstration then started, with people chanting: "With our soul, with our blood, we shall sacrifice for Bashar," in reference to Syrian President Bashar al-Assad.
Since mass uprisings overthrew Egyptian President Hosni Mubarak and Tunisia's Zine al-Abidine Ben Ali, Syrian authorities have intensified a long-running campaign of arrests of dissidents, independent writers and opposition figures.
There are an estimated 3,000-4,000 political prisoners in Syria, mostly held without trial. They include Kurds, Islamists and secular figures who have been demanding a democratic system to replace the Baath Party's five decade monopoly of power.
On Tuesday about 40 people joined a protest in Damascus, briefly chanting political slogans in the first challenge to the ruling party since civil unrest gripped the Arab Middle East.
New York-based Human Rights Watch has said Syria's authorities were among the worst violators of human rights in 2010, jailing lawyers, torturing opponents and using violence to repress ethnic Kurds.
(Additional writing by Yara Bayoumy and Dominic Evans; Editing by Peter Graff)