Thousands of women staged a sit-in Wednesday on a main highway in northeastern Syria to demand the release of hundreds of people arrested in protest towns in the region, a rights activist said.

"More than 5,000 women are gathered on the main road linking the towns of Tartus and Banias to demand the release of hundreds of people arrested yesterday in Baida by security forces," Rami Abdel Rahman told Agence France Presse.

Armed gangs were responsible for preventing injured security forces victims of pro-reform protests receiving medical treatment, Syrian authorities said on Wednesday.

"Certain media have compiled baseless accusations saying the Syrian authorities prevented the injured from going to hospital for treatment," an Interior Ministry statement said.

At least seven people were killed in Yemen, including four police who clashed with a dissident army unit, military sources and medics said on Wednesday.

"Police attacked an army checkpoint in Amran province," 170 kilometers north of Sanaa late on Tuesday, "killing one officer and wounding two soldiers," a military official told Agence France Presse.

Egypt's ex-president Hosni Mubarak has been placed in detention for 15 days, prosecutors said Wednesday shortly after state media reported his two sons had also been detained.

In a statement on the public prosecutor's Facebook page, a spokesman said the prosecutor Abdul Maguid Mahmoud authorized the detentions "as part of an inquiry into the use of force against protesters during the unrest in January and February."

Gulf Arab states have demanded the cancelation of an Arab summit due in Baghdad next month, Bahrain's official BNA news agency quoted the foreign minister as saying on Tuesday.

"Gulf Cooperation Council countries have demanded that the Arab summit which is due to be held in Iraq be cancelled," BNA quoted Sheikh Khaled bin Ahmed al-Khalifa as saying.

The White House condemned escalating repression of demonstrations in Syria Tuesday as "outrageous" and expressed concern about reports that the wounded were being denied medical care.

"We are deeply concerned by reports that Syrians who have been wounded by their government are being denied access to medical care," press secretary Jay Carney said in a statement.

Syrian security forces locked down the protest flashpoint town of Banias and raked the nearby village of Baida with gunfire on Tuesday, witnesses told Agence France Presse by telephone.

"Security forces and armed men are firing machine guns indiscriminately at the village," a witness said.

Syrian security forces in at least two towns prevented medics from reaching wounded protesters when clashes erupted at anti-government demonstrations last week, Human Rights Watch (HRW) said.

The New York based rights group said the "inhumane" and "illegal" blocking of access to medical treatment occurred in the southern town of Daraa, the center of a wave of protests against President Bashar al-Assad, and Harasta near Damascus.

Britain and France called on NATO allies Tuesday to pull their weight in the bombing mission in Libya in a sign of growing disquiet over the campaign as the conflict drags on.

NATO has led air strikes against Moammar Gadhafi's forces for almost two weeks since taking control of the operation from a U.S.-led coalition that had been bombing the regime's heavy weaponry since March 19.

Britain warned Tuesday against all but essential travel to Syria after a bloody weekend crackdown on anti-regime demonstrators.

"In light of the deteriorating security situation in Syria we have decided to change the overall level of our travel advice: we now advise against all but essential travel to Syria," Foreign Office Minister for Middle East and North Africa Alistair Burt said.