The Local Coordination Committees of Syria alleged prison officials cleaned the facility in Homs, repaired heating and lighting and improved the overall living conditions in advance of the visit by the monitors sent to Syria last month, CNN reported.
The opposition group also claimed that five people were killed by government forces. The LCC said government security troops were bombarding Daraya, a Damascus suburb, with helicopters, tanks and busloads of troops.
Foreign news organizations cannot independently verify events reported from inside Syria because of government restrictions on journalists.
Arab League Secretary-General Nabil el-Araby was expected to be briefed on the situation in Syria from the head of the Arab Human Rights Council Wednesday.
On Tuesday, French and U.S. officials said they had doubts about whether Syria was abiding by its agreement with the Arab League, which calls for the release of anti-government protesters and the withdrawal of Syrian troops from cities, among other things.
In Paris, French Foreign Minister Alain Juppe said he was "a little skeptical" about whether the monitors had free access as President Bashar Assad's regime pledged.
In Washington U.S. State Department spokeswoman Victoria Nuland acknowledged that some progress has been made since Assad agreed to an Arab League plan to reduce violence, but said more needed to be done.
Several organizations estimate between 5,000 and 6,000 deaths have occurred since the government crackdown on protesters 10 months ago. Assad's regime said it is cracking down on armed terrorists.