BEIRUT - The Syrian army has recaptured most of the northern rebel stronghold of Idlib near the Turkish border, pushing hundreds of military defectors out of a major base they had held for months even as pockets of resistance kept up their fight on Tuesday.

The three-day operation to capture the city followed closely after a similar offensive to dislodge the opposition from another key piece of territory it had controlled, the Baba Amr district in central Homs. The two victories gave President Bashar Assad's regime unmistakable momentum as it tries to crush the armed opposition fighters.

A pledge Tuesday from Syria's staunch ally Russia that Moscow will continue selling weapons to the regime was yet another boost. And a diplomatic bid by U.N. envoy Kofi Annan to broker a cease-fire and start negotiations failed over the weekend.

Still, international pressure is more intense than ever, with the U.S. considering military options. On Tuesday, the Arab League chief said the regime's killing of civilians amounts to crimes against humanity and he called for an international inquiry.

Activists reported fresh violence in central province of Hama near Homs, the suburbs of Damascus and elsewhere, killing dozens.

New York-based Human Rights Watch said troops have planted land mines near its borders with Turkey and Lebanon along routes used by people fleeing the violence and trying to reach safety in neighbouring countries. HRW said its report was based on accounts from witnesses and Syrian deminers and that the land mines have already caused civilian casualties.

"Any use of anti-personnel land mines is unconscionable," said Steve Goose of Human Rights Watch. "There is absolutely no justification for the use of these indiscriminate weapons by any country, anywhere, for any purpose."

In November, a Syrian official and witnesses told The Associated Press that Syria planted land mines along parts of its border with Lebanon. The official claimed at the time that the mines aimed to prevent arms smuggling.

HRW quoted a former Syrian army deminer as saying that in early February, he visited the border town of Hasanieih and found land mines planted "between the fruit trees three meters (yards) from the border in two parallel lines, each approximately 500 metres (yards) long."

HRW also quoted a resident of the border town of Kherbet al-Joz as saying that for 20 days, until March 1, he saw some 50 soldiers accompanied by two large military vehicles putting land mines starting from Kherbet Al-Joz toward two other villages. Both Kherbet al-Joz and Hasanieih border Turkey in the north.

Fresh from a monthlong campaign that drove rebels out of Baba Amr in the city of Homs, Assad's forces launched a siege on the Idlib three days ago. The city largely had been under control of hundreds of fighters for the rebel Free Syrian Army.

The pro-government Al-Watan daily and the Britain-based Syrian Observatory for Human Rights said government troops were in control of Idlib on Tuesday. The Observatory said the army was still facing some resistance pockets in three Idlib areas, including the central neighbourhoods of Dubait and Bustan Ghanoum.

Idlib, a predominantly Sunni city of some 150,000 people located about 100 miles (160 kilometres) north of Homs, was among the first to fall in the hands of army defectors last summer. Rebels were in control of a large parts of the city in the past months with troops present in some areas.

Calls to the area were not going through, making it difficult to confirm the events of the past few days. But witnesses have said this week that army defectors in the city have been running out of ammunition.

Many feared the offensive in Idlib could end up like the regime's campaign against Baba Amr. Troops besieged and shelled Baba Amr for almost a month before capturing it on March 1, after hundreds of civilians were killed. Activists accused the regime of atrocities after the military captured Baba Amr.

The Free Syrian Army, made up of army defectors and protesters who have taken up weapons, has been dealt two major defeats. But the conflict is far from over. The FSA has appealed for outside help in getting weapons to help the group put up a fight.

An influx of weapons could transform the conflict. Saudi Arabia and Qatar have been discussing military aid, but the U.S. and others have not advocated arming the rebels, in part out of fear it would create an even more bloody and prolonged battle. Syria has a complex web of allegiances in the region that extend to Iran and the Lebanese militant group Hezbollah, raising fears of wider violence.

But Damascus can be sure of a steady supply of army from Russia.

On Tuesday, Russian Deputy Defence Minister Anatoly Antonov said Russia will abide by existing contracts to deliver weapons to Syria despite Assad's yearlong crackdown.

Arab League chief Nabil Elaraby said it would not be ethical or moral to allow those behind the killings in the cities of Homs and Idlib to get away with their crimes.

"There must be an impartial international inquiry into what is happening to uncover those responsible for these crimes to face justice," he said in Cairo.

In northern Syria, the Observatory and another activist group, the Local Coordination Committees, reported intense clashes between government troops and rebels in the town of Maaret al-Numan, in Idlib province, on Sunday night.

The U.N. refugee agency said 230,000 Syrians have fled their homes since the uprising against Assad's regime began last year. The U.N. says more than 7,500 people have been killed in the past 12 months.

Panos Moumtzis, the UNHCR's co-ordinator for Syria said 30,000 people have already fled to Turkey, Lebanon and Jordan and "on a daily basis hundreds of people are still crossing into neighbouring countries."

Moumtzis said at least 200,000 people were also displaced within the country, according to the Syrian Arab Red Crescent.

Assad has made a series of gestures toward reform to try to allay the crisis, but his opponents say his efforts are too little, too late. On Tuesday, he set nationwide parliamentary elections for May 7. The vote was initially to take place in March but was postponed after last month's referendum on the country's new constitution that allowed new political parties to run.

U.S. State Department spokeswoman Victoria Nuland dismissed the vote as meaningless.

"Parliamentary elections for a rubber-stamp parliament in the middle of the kind of violence that we're seeing across the country is ridiculous."