GENEVA - Government forces in Syria on Tuesday called on opposition fighters in Aleppo to drop their weapons and surrender to authorities as they captured new ground on the northwestern edge of the city, tightening the siege on rebel-held parts of the metropolis where some 300,000 people live, activists said.

The push in which troops captured large parts of the city's Layramoun area came as state TV reported that the General Army Command informed residents of rebel-held parts of Aleppo via telephone text messages that the army has created several safe passages and makeshift centers for whoever wants to leave those areas.

The army said it will keep providing Aleppo residents with basic necessities, but called all those living in rebel-held parts of the city to kick out "mercenaries and foreign fighters."

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In Geneva, the U.N. envoy for Syria said he aims to call a new round of talks between government and opposition envoys in Geneva "toward the end of August."

Staffan de Mistura said he wants to see the outcome of steps agreed upon in Moscow last week between the United States and Russia, in order "to make these talks particularly fruitful and hopeful" before setting a precise date.

The U.N. envoy spoke to reporters Tuesday after a closed-door meeting in Geneva with high-level U.S. and Russian diplomats. He said the discussion centered on initiatives about the "urgent need" for progress on issues like a widely violated ceasefire, humanitarian access, counter-terrorism and political transition in Syria.

Syrian government forces and their allies have been on the offensive around the Aleppo, Syria's largest city and former commercial center, for weeks. Since earlier this month, they have tightened their siege and residents in rebel-held parts have been reporting food shortages.

The Britain-based Syrian Observatory for Human Rights and the Local Coordination Committees reported intense fighting and airstrikes before the capture of the Layramoun area.

The Lebanese group Hezbollah's Al-Manar TV aired footage of government forces pushing in what appeared to be an industrial area near Aleppo. The station confirmed that President Bashar Assad's forces capture of areas in Layramoun and near Castello road, the main link between rebel-held parts of Aleppo and the rest of the country.

Earlier Tuesday, Russian Foreign Minister Sergey Lavrov said that recent U.S.-Russia discussions should encourage moderate Syrian opposition groups to leave areas occupied by al Qaeda's branch in Syria, thus helping to implement a truce. Lavrov spoke to Russian news agencies after talks in Laos with U.S. Secretary of State John Kerry, who visited Moscow earlier this month.

Moscow and Washington have differed over the role of the local al Qaeda branch known as the Nusra Front, with Russia calling the group terrorists and the U.S. asking Russia not to target them for fear of hitting the moderate opposition.

The U.S. has offered Russia a military partnership in Syria that includes intelligence and targeting sharing and even joint bombing operations.

The proposal would address the Nusra Front, which has presented one of the most persistent obstacles in enforcing a cease-fire in Syria. The group is engaged in a variety of local alliances with other rebel groups the U.S. and its Arab allies want shielded by the cessation of hostilities. The al Qaeda affiliate's fighters are often embedded with such groups on the battlefield or move between various militant formations.

The dispute over the Nusra Front has undermined the Russia- and U.S.-brokered truce with fighting continuing to rage in many areas in Syria. It has also fueled speculation of a potential split between Nusra and al Qaeda for practical purposes.

A Nusra Front official told The Associated Press on Tuesday that the group's leader Abu Mohammed al-Golani plans to announce a disassociation with al Qaeda soon. Speaking via text message from northern Syria, the official, who spoke on condition of anonymity because he was not authorized to speak publicly about the issue, said Nusra will merge with other insurgent groups.

Nusra Front is one of al Qaeda's most powerful branches around the world and reports about a possible disassociation with al Qaeda have circulated in the past but never materialized.

Some Nusra Front supporters said on social media that Nusra Front will change its name to The Front to Conquer the Levant. The activists even posted what they said is the group's new purported banner: White instead of black with the Muslim shahada on top and below it The Front to Conquer the Levant will replace the Nusra Front.