BEIRUT (AP) — The al-Qaeda-breakaway Islamic State of Iraq and the Levant has prevented food and medical supplies from reaching some neighborhoods in an eastern Syrian city and has ceased some of its operations in Syria while waiting for weapons to arrive from neighboring Iraq, activists said Friday.

The Britain-based Syrian Observatory for Human Rights said the siege is mostly on rebel-held neighborhoods of Deir el-Zour. It said an offensive by the Islamic State in eastern Syria against rival Islamic rebel factions has killed more than 640 people and uprooted at least 130,000 since the end of April.

The Islamic State of Iraq and the Levant’s campaign in the oil-rich Deir el-Zour province appears aimed at linking the large expanse of territory under its control in northern and eastern Syria with areas it has captured in neighboring Iraq. It seized that country’s second largest city of Mosul and other areas earlier this week in a lightning advance toward Baghdad.

The Observatory’s chief Rami Abdurrahman told The Associated Press that most operations by the Islamic State in Syria appear to have been suspended until weapons arrive from Iraq, where its fighters captured large amounts of ammunition, arms and vehicles.

Abdurrahman said Islamic State fighters have not fought major battles for the past two days except for some skirmishes in the northern province of Aleppo. He added that some Humvees apparently seized in Iraq have already appeared in the northern Syrian town of Manbij, which is under the control of the Islamic State.

The group, which is largely composed of foreign jihadists, has made significant headway in Syria over the past six weeks, seizing towns and villages in heavy fighting against the al-Qaeda-affiliated Nusra Front and other Islamic rebel groups.

The Islamic State recently captured a bridge on the Euphrates river that was the main entrance to rebel-held parts of Deir el-Zour, which is contested by the rebels and government forces, the Observatory said.

An activist based in Deir el-Zour, who goes by the name of Abu Abdullah, said via Skype that some food is being smuggled into the city by boat. He added that food prices have already started rising.

“A humanitarian crisis is beginning in the city,” Abu Abdullah said.

The Britain-based Observatory, which relies on a network of activists inside Syria, said the Islamic State is preventing vehicles from entering or leaving the neighborhoods, which are home to 25,000 people.

“Some residents have informed activists with the Observatory that there is food only to keep residents inside the city alive,” it said.

The Observatory and Abu Abdullah said Nusra Front fighters crossed the border crossing point of al-Bukamal into the Iraqi town of Qaim Thursday and captured five Humvees and three armored personnel carriers after Iraqi troops abandoned their positions on the border. They said that the vehicles were brought into Syria.

Abdurrahman added that Syrian government helicopter gunships destroyed one of the armored personnel carriers Friday in al-Bukamal that is near Deir el-Zour.

Syrian government forces and rebels have besieged several areas over the course of the three-year civil war in a bid to starve out their opponents, a tactic that has been condemned by the United Nations and human rights groups.

Also Friday, the Observatory reported that six fighters from Lebanon’s Shiite Muslim Hezbollah group were killed in clashes with Syrian rebels in the suburbs of the capital Damascus. It said they were killed on Thursday.

In Lebanon, news websites close to Hezbollah, which openly joined Syrian President Bashar Assad’s forces in Syria’s civil war last year, confirmed six fighters were killed “while performing their jihadi duties.” They gave no further details.

Copyright 2014 The Associated Press