Correction: Earlier versions of this article said the Arab League monitors had also visited the city of Deraa. The article has been corrected.

A rare visit by foreign officials inside the increasingly desperate Syrian city of Homs was met Tuesday by frantic pleas from residents amid a crackdown against protesters by forces of President Bashar al-Assad.

The arrival of the delegation of observers from the Arab League in the centrally located city marked one of the few chances for embattled Syrians to make their case directly to the outside world. Many people complained that violence continued to rage despite the monitors’ presence and that the international community had done too little to protect them during the nine-month-old uprising.

“We are unarmed people who are dying,” shouted one man, shown in a video uploaded to YouTube on Tuesday, as he accosted some of the 50 observers now in the country. He asked them to go deeper into the city and pointed out out pools of blood and shattered buildings. “Where is the world?” asked a man in another video.

Opposition groups had called for the Arab League to send a team to Homs, regarded as a center of the uprising, to monitor whether Syrian authorities were sticking to an agreement to withdraw soldiers from populated areas and stop using deadly force against protesters.

Just before the visit, army tanks withdrew from the city or were hidden in government buildings, and snipers on the rooftops exchanged their uniforms for civilian clothes, said Saleem Qabani, a protester reached by Skype. He added that he saw soldiers near a security checkpoint changing into police uniforms.

Syria has imposed strict limits on reporters in the country, making it impossible to independently confirm his and other reports.

As the monitors visited the hard-hit Homs neighborhood of Baba Amr, tens of thousands of people gathered in the streets and headed toward Clock Square in the city center to demand the ouster of Assad, said Rami Abdulrahman of the London-based Syrian Observatory for Human Rights.

At the demonstration, the largest in the city since the summer, observers were able to see security forces firing on the crowd, Qabani said. “The massacre committed was in front of their eyes, so their visit did not change anything,” he said.

Anti-government activists say that more than 100 people have been killed by security forces in Homs in the past week and that areas including Baba Amr have been surrounded by hundreds of tanks, which have been shelling residential areas, while food, fuel and medicine run low. Some elements of the opposition in Homs have taken up arms, allying themselves with the loose group of army defectors and rebels known as the Free Syrian Army.

“The regime used the last several days as an opportunity to escalate their attacks on several . . . neighborhoods in Homs and other cities prior to the deployment of these monitors,” State Department spokesman Mark Toner said Tuesday in Washington.

Toner also expressed hope that the monitors would be able to do their work. “We obviously look to these individuals to be intrepid in their search for the truth of what’s happening on the ground,” he said. He said the United States “would . . . demand that the Syrian authorities allow them full access to the Syrian people in order to carry out their mission.”

The observers are traveling with Syrian security forces, raising doubts for those in the opposition about whether they will be able to monitor the situation effectively. The relatively small number of monitors has also prompted some opposition leaders to dismiss the mission as a waste of time. A contingent of 500 was initially discussed, but only 150 are now likely to enter the country, according to Wissam Tarif, a rights activist with the Avaaz movement.

“This mission was born dead,” said Tarif, who was initially nominated by the Arab League as a monitor but withdrew because of concerns about the operation.

Human Rights Watch reported Tuesday that security sources said in interviews with its researchers that political detainees in Homs were being transferred out of prisons ahead of the Arab League visit.

However, the Syrian National Council, an umbrella opposition group whose members are mostly outside Syria, said the fact that observers had witnessed a protest and been allowed into the troubled Baba Amr neighborhood was a sign that they had been exposed to the true nature of the unrest.

Bassma Kodmani, spokeswoman for the group, said its members had been providing guidance to the Arab League team on areas to visit, identifying places where activists allege that security forces have cracked down on protests.

“We have all sorts of doubts and apprehensions about the mission, but we have supported it as much as we can,” she said.

She said that the observers had asked to visit several cities where protests and clashes had taken place and that the next step would be for the Arab League to meet and decide whether to refer the situation to the U.N. Security Council. Some observers walked around parts of Homs without escorts and met with leading figures from the local opposition movement, eyewitnesses said.

The unrest has threatened to spill into neighboring countries, with at least two violent border incidents reported Tuesday. Three Lebanese men were shot dead by Syrian security forces with heavy machine guns on Syrian territory near the border with Lebanon — where many people mistrust Syrian authorities — according to the Lebanese national news agency. In addition, Syrian state media reported that security forces had killed several “terrorists” attempting to enter the country from Turkey.

An explosion at an oil pipeline outside Homs on Tuesday threatened the main power station in the area, jeopardizing an already shaky electricity supply. Medical supplies are said to be running short, and in some areas residents report that dead and wounded people lie in the streets, with soldiers preventing all movement.