|Thousands have taken to the streets across Syria since protests began in March [EPA]
A prominent rights activist has said Syrian authorities have arrested more than 1,000 people in their latest security sweep.
Ammar Qurabi, the head of the National Organisation for Human Rights in Syria, said on Tuesday that his group had documented about 1,000 names of people who were detained across Syrian provinces in door-to-door raids since Saturday.
In-depth coverage of escalating violence across Syria
He said many other people had been reported missing.
Separately, Al Jazeera is demanding information about one of its journalists who has been missing in Syria since Friday afternoon.
Dorothy Parvaz left the Qatari capital, Doha, for Syria to cover events in the country. However, there has been no contact with the reporter since she disembarked from a Qatar Airways flight in Damascus.
Over the past week, the government of President Bashar al-Assad has intensified a campaign to quell the unrest in the country.
Soldiers and tanks have been deployed in cities including Deraa in the south, which has been shelled and put under siege.
Activists said security forces forced their way into houses on Sunday in the old quarter of the city, and took away many men under 40.
Arrests have also been reported in the capital, Damascus, the nearby towns of Zabadani and Madaya and in Qamishli in the east.
'Urgent medical needs'
The Red Cross on Tuesday urged Syria to immediately lift restrictions on access to casualties in Deraa, the epicentre of the crackdown on pro-democracy protests.
"The violence has resulted in a large number of casualties and we fear that if the situation worsens, more lives will be lost," Marianne Gasser, head of the International Committee of the Red Cross (ICRC) delegation in Damascus, said.
"It is urgent that emergency medical services, first aid workers and others performing life saving tasks swiftly reach those in need," she added in a statement.
ICRC spokesman Hisham Hassan said the doctors and staff from the agency Syrian Red Crescent and other medical workers needed "immediate access to the injured".
"So far we have had restricted access to certain areas, however today we need to have more larger access especially in the south, and here I talk about Deraa," he told journalists.
"We are in touch with Syrian authorities on a daily basis but so far what we have been able to get is access probably tomorrow or the day after to certain hospitals in rural Damascus, but so far no news about Deraa in the south."
Activists say food, water and medical supplies are in short supply in the city, where electricity and communications have been cut since April 26, and have called on Syrians to protest every day at noon in solidarity with the city.
Syria's government accuses "armed groups and terrorists" of attempting to stir unrest. In a statement on Sunday evening, the interior ministry offered an amnesty for citizens caught up in the revolt to hand themselves in.
The ministry told "citizens who have participated in or committed unlawful acts such as bearing arms, attacking security or spreading lies to surrender by May 15 and hand their weapons in to the competent authorities".