SANA, Associated Press
In this photo released by the Syrian official news agency SANA, Syrian president Bashar Assad, right, speaks with Iraqi Foreign Minister Ibrahim al-Jaafari, left, in Damascus, Syria, Tuesday, March. 24, 2015. Al-Jaafari said they discussed “Syrian and Iraqi issues, and the common dangers that threaten our security.”

BEIRUT — Syrian rebels launched an offensive Tuesday against a major government-held city in the country's northwest, shelling the outskirts and warning residents to remain indoors in the coming days.

The target of the operation is Idlib, a city of some 165,000 people and the provincial capital of a province with the same name. Opposition fighters have controlled the countryside and towns across the province since 2012, but President Bashar Assad's forces have maintained their grip on Idlib city.

Activists said Syrian government helicopters attacked the nearby town of Binish with chlorine gas Tuesday night. The Local Coordination Committees did not give details about casualties but Muayad Zurayk, an activist based in Idlib province, said 30 people were rushed to the hospital after suffering breathing problems.

The alleged attack came a week after the opposition claimed that the government carried out a poisonous gas attack on the nearby town of Sarmin, killing six and wounding dozens. Damascus denied the allegation.

Armed opposition factions announced the campaign to capture Idlib in a message posted online Tuesday. They told residents that the rebels "are at the walls of Idlib" and "have decided to liberate this good town." The message also asked locals to remain indoors in the coming days.

Syrian state TV quoted an unnamed military official as saying that government forces are repelling "attempts by terrorist groups to infiltrate the outskirts" of Idlib. The official said clashes were ongoing, adding that troops inflicted "heavy losses" on the attackers. The government refers to the rebels as terrorists.

Zurayk, the activist based in Idlib province, said the offensive began Tuesday morning and was being led by several factions including al-Qaida's branch in Syria, the Nusra Front, as well as the ultra-conservative Ahrar al-Sham and Jund al-Aqsa groups.

"The rebels have captured five checkpoints so far and are getting close to the gates of Idlib," Zurayk said via Skype. He said rebels are advancing from four directions, adding that there were two suicide car bombs in the afternoon that targeted an army base near the city.

He said the operation to capture the city is dubbed "Fatah Army," adding that two opposition fighters have been killed and several others wounded.

The Britain-based Syrian Observatory for Human Rights said rebels are shelling the city, but have yet to try to push into Idlib itself. The Idlib Media Center also said the rebels are targeting government positions on the city's outskirts.

Observatory director Rami Abdurrahman said the opposition groups involved in the operation include the Nusra Front as well as Islamist rebel factions. The Observatory said rebels shelled the city, killing and wounding about 15 people.

Rebels have tried in the past to enter the city of Idlib but did not succeed.

More than 220,000 people have been killed since the conflict in Syria began in March 2011. The crisis started with largely peaceful protests calling for reforms and escalated into civil war following a brutal government crackdown.

Meanwhile, in Damascus, Iraq's visiting foreign minister held talks with Assad that focused on threats facing both countries, including the Islamic State group. Assad said coordination and consultations between the two countries would bolster successes against militants, the state news agency SANA reported.

Iraqi Foreign Minister Ibrahim al-Jaafari said they discussed "Syrian and Iraqi issues, and the common dangers that threaten our security." He told reporters he hopes to boost Iraq-Syria ties to defeat those threats. Al-Jaafari also met with his Syrian counterpart, Walid al-Moallem, during the visit.

The Islamic State group has seized about a third of both Syria and Iraq.

The Observatory said Kurdish gunmen killed at least 28 Islamic State fighters in a special operation in the northern province of Raqqa. It added that members of the main Kurdish militia, the People's Protection Units, or YPG, were able to capture the bodies of the dead militants.

YPG fighters have been battling the IS group for months, capturing scores of villages. The Kurds blamed IS for two bombings last week that killed 49 people celebrating the Kurdish New Year in the northeastern Syrian city of Hassakeh.

Also Tuesday, Russian Ambassador to the United Nations Vitaly Churkin said the next round of Syria talks in Moscow will be between April 6 and 9. The first round of Moscow peace talks was held in January and boycotted by most rebel groups as well as the main Western-backed Syrian National Coalition. Russia is a key ally of Assad's government.

Associated Press writers Bassem Mroue in Beirut, Cara Anna at the United Nations, and Albert Aji in Damascus, Syria contributed to this report.