(CNN) -- Syrian troops shelled restive neighborhoods Saturday during a massive push in the city of Homs, activists said.
An onslaught occurred in the flashpoint neighborhood of Bab Amr, said activists Abu Omar, based in the western city, and Alexander Page, speaking to CNN from Cairo, where he is in touch with people in Homs. Omar and Page said thousands of troops entered Homs.
"They are surrounding the area from everywhere," Omar said. As CNN spoke to him by phone, heavy gunfire could be heard in the background.
The operation occurred as the Arab League prepared to start its monitoring mission next week, part of an initiative to end the violence in Syria.
Another activist in Homs, Abu Salim, said at least 4,000 security personnel were surrounding Bab Amr and the number was increasing. The troops dug trenches around parts of the neighborhood.
He said the neighborhood's population before the security forces arrived was at least 50,000. Now, many people have fled, fearing death and escaping the harsh humanitarian conditions.
"Much of the shelling in the city is coming from the local headquarters of military intelligence in the city. They shell different neighborhoods from there," Salim said. "Tanks are present in some neighborhoods and they directly shoot at homes."
Salim said people are targeted if they walk the streets, there are shortages of fuel, heating oil and baby formula, and "the humanitarian situation is really difficult."
"The sounds of explosions are almost continuous and rarely stop even through the night," he said.
Salim said makeshift medical clinics are trying to make do.
"We lack any sophisticated medical tool or equipment. ... We only use first aid kits and tools to deal with bullet wounds. Most of the wounded end up dying. ... We do not have enough doctors or nurses to help the injured," he said.
Omar said he saw more than 40 injured people at a field hospital. Asked why he thinks security forces are targeting Bab Amr, he said the neighborhood is staunchly against Syrian President Bashar al-Assad and is "making a lot of problems for the regime."
He asked the international community for its support.
"We want your help. ... We just need a no-fly zone, and more pressure on al-Assad's regime," Omar said.
At least five neighborhoods in Homs have been attacked, Salim said.
Security forces also shelled the neighborhoods of Bayada, Khaldiyeh, and Karm Al-Zaitoun, and warplanes flew over the area, according to the Local Coordination Committees of Syria (LCC), an opposition activist network.
The LCC said 38 people were killed across the country Saturday, including 25 in Homs.
It also said security forces assassinated Ghazi Mohammad Khaled Zoaib, former secretary general of the Homs' division of the Baath Party, and his wife, Rajaa Mohammad Khaled Bakkar. That incident occurred during a raid on their house in Bab Amr.
"The martyr had been threatened before by the regime as a result of his support of the revolutions since its beginning," the LCC said.
It said two army defectors were also killed. A massive demonstration was taking place in the neighborhood of Malaab, a protest in solidarity with the people of Bab Amr.
CNN cannot independently verify reports of deaths and injuries in Syria. The Syrian government has restricted access to international journalists.
The attacks in Homs came a day after dual bombings struck the country's capital, Damascus. Al-Assad's government blamed terrorists inside and outside of Syria, but the opposition called the attacks the work of the regime.
Syria has entered its bloodiest period in a months-long uprising, raising questions about whether observers from the Arab League will be able to stem the growing violence.
The United States, which has called for al-Assad to step aside and has initiated sanctions against the regime, deplored the bombings, said there "is no justification for terrorism of any kind" and expressed hope that the strike doesn't undermine the Arab League efforts.
"It is crucial that (the) attack not impede the critical work of the Arab League monitoring mission to document and deter human rights abuses with the goal of protecting civilians," State Department deputy spokesman Mark Toner told reporters Friday.
"We hope that this mission will proceed unfettered in an atmosphere of non-violence. The burden is on the regime to cooperate fully and quickly with the monitoring mission."
More than 5,000 people have died since al-Assad began a brutal crackdown in mid-March on anti-government protesters calling for his ouster, the United Nations said earlier this month.
Many more deaths have since been reported. AVAAZ, a New York-based political activist group, and the LCC said more than 6,000 people have been killed.
The Syrian government has said 2,000 of its soldiers and security forces have been killed in the uprising, which it blames on "armed gangs."
A surge of violence this week claimed almost 300 lives, according to the opposition Syrian National Council.
Funerals occurred Saturday for 44 people killed in the two suicide car bombings at the offices of two security branches in Damascus, the Ministry of Interior said in a statement released to the state-run Syrian Arab News Agency. At least 166 were wounded in the attack, the ministry said.
The violent crackdown by al-Assad's security forces against the opposition has garnered worldwide condemnation from the European Union, the Arab League and Turkey in addition to the United States.
CNN's Samira Said, Mohamed Fadel Fahmy and Salma Abdelaziz contributed to this report.