BEIRUT — Syrian forces intensified their crackdown on an eastern city Sunday as they try to keep the anti-government uprising from escalating during the Muslim holy month of Ramadan. The assault and similar operations in at least two other towns killed at least 59 people, according to human rights groups, and the toll looked likely to rise.

The worst violence was in the eastern city of Deir el-Zour, where troops stepped up a siege that had already been going on for days. At least 42 people were killed in a raid on the city that began before dawn, said Abdul-Karim Rihawi, the Damascus-based chief of the Syrian Human Rights League and Ammar Qurabi, who heads the National Organization for Human Rights in Syria.

“Humanitarian conditions in the city are very bad because it has been under siege for nine days,” one activist in Deir el-Zour said on condition of anonymity for fear of reprisals. “There is lack of medicine, baby formula, food and gasoline. The city is totally paralyzed.”

The attack on Deir el-Zour is part of the latest phase of the government crackdown that began a week ago, just before the start of Ramadan when many Muslims fast from dawn to dusk, then eat festive meals and gather in mosques for special nightly prayers. The government has been trying to prevent the large mosque gatherings from turning into a new wave of anti-government protests, like those that have been sweeping the country since mid-March.

The central city of Hama had been the focus of the crackdown for most of the week, though Deir el-Zour has also been under siege.

In Hama, an official at Hourani Hospital reported that eight newborns died in their incubators on Wednesday when electricity was cut in the city, the London-based Syrian Observatory for Human Rights said. The group had no further details.

Authorities have imposed a media blackout on Hama and the reports could not be immediately confirmed. Electricity, Internet and phone lines have been cut for seven days, and residents have reported dwindling food and medical supplies amid frequent shelling and raids. Rights group say at least 100 people have been killed, while some estimates put the number as high as 250.

Authoritarian President Bashar Assad has defied a growing chorus of international condemnation and pressed on with lethal military force to suppress mostly peaceful, unarmed demonstrators.

U.N. Secretary General Ban Ki-Moon on Saturday urged Assad, in a phone conversation, to immediately stop the use of military force against civilians.

Turkey, which borders Syria, said Sunday it would send its foreign minister to Damascus on Tuesday to deliver a strong message against the crackdown on the protesters. Turkish Prime Minister Recep Tayyip Erdogan said his country’s patience was running thin and that Turkey could not remain a bystander to the violence.

Syria’s reaction was quick. State-run TV quoted Assad’s adviser, Buthaina Shaaban, as saying that Turkey’s foreign minister “will hear stronger words because of Turkey’s stance that did not condemn until now the brutal killings of civilians, members of military and police.”

Gulf Arab countries broke their silence Saturday on the bloodshed, calling for an immediate end to the violence and for the implementation of “serious” reforms in Syria. In a statement posted on its website, the six-nation Gulf Cooperation Council expressed deep concern and regret for “the escalating violence in Syria and use of excess force.”

Syria’s state-run TV quoted an unnamed official as saying the GCC statement was ignoring the sabotage that armed groups are conducting.