BEIRUT (AP) -- Syrian government troops launched an assault Wednesday to regain control of a northern village that was the site of an alleged chemical weapons attack earlier this year, activists said.

The push on Khan al-Assal, a village on the southwestern outskirts of the embattled city of Aleppo comes just over a week after it was captured by the rebels.

The capture was a rare success for the rebels on the battlefield as opposition forces recently suffered two major setbacks during a wide-ranging government offensive in central Syria. In June, President Bashar Assad's army recaptured the strategic town of Qusair near the Lebanese border and earlier this week, government troops took control of a district in the city of Homs that has been the opposition stronghold since the beginning of the conflict, now in its third year.

The Britain-based Syrian Observatory for Human Rights said 150 soldiers were killed after Khan al-Assal fell to the rebels.

The Observatory said the army on Wednesday attacked rebel positions outside the village, after first bringing in reinforcements to the area.

Khan al-Assal was the scene of a purported chemical attack on March 19 that killed at least 30 people. Assad's regime and the rebels fighting to topple it have blamed each other for that attack.

Last week, the government indicated it agreed with a U.N. team on a possible investigation into chemical attacks. It was the first time U.N. weapons experts had visited Damascus since allegations surfaced that chemical agents have been used in Syria's conflict.

A joint statement Saturday by the Syrian foreign ministry and the U.N. team said the parties agreed ``on ways of moving forward,'' without saying if there would be an investigation and whether it would be limited to Khan al-Assal.

Assad's government has previously agreed that the U.N. investigate only the Khan al-Assal attack and refused to have a possible inquiry include other alleged chemical attack sites in Homs, Damascus and elsewhere.

The United States has backed the opposition in Syria's conflict and has called on Assad's regime to grant the U.N. team unfettered access to investigate all allegations of chemical weapon use.

Earlier this month, the U.N. said it has received 13 reports of alleged chemical weapons use in Syria.

Khan al-Assal was under government control in March but was captured by the rebels on July 22. Even if the U.N. team is granted access to the village, it may be difficult to find evidence from the March attack because so much time has passed.

In June, the U.S. said it had conclusive evidence that Assad's regime used chemical weapons against opposition forces. That crossed what President Barack Obama called a ``red line,'' prompting a U.S. decision to begin arming rebel groups, although that has not happened yet.

Russia, Syria's close ally, has called the chemical weapons allegations against Assad's regime groundless, claiming Russian experts have determined that Syrian rebels made sarin nerve gas and used it in the Khan al-Assal attack.