Recapturing the Abu Zuhour air base, which the rebels took in 2015, has been one of the main goals of the government offensive launched in late October. The operations also aim to secure the road linking the capital, Damascus, with the northern city of Aleppo, Syria's largest.
The government-controlled Syrian Central Military Media said troops are fighting al-Qaida-linked militants and other insurgents in different areas near Abu Zuhour. It said troops approaching from the south are now 2 km away from the base.
The government offensive has displaced tens of thousands of people, who have fled toward areas close to the Turkish border.
The push into Idlib province, which is mostly held by rebels, is the deepest by the government since it lost much of the area three years ago.
The UN human rights chief Zeid Ra'ad Al Hussein expressed "grave concern" over the situation in Idlib, which is home to more than 2.6 million Syrians, including more than 1.1 million who fled fighting elsewhere in the country.
Zeid also condemned the upsurge in civilian casualties in the eastern suburbs of Damascus known as eastern Ghouta, stressing that all parties are obliged under international law to distinguish between lawful military targets and civilians.
Today, more than two dozen people were killed in the government bombardment of eastern Ghouta and rebel shelling of the capital itself.
"The suffering of the people of Syria knows no end," Zeid said in a statement about eastern Ghouta, where nearly 400,000 people are living under government siege.
"In Idlib, ground attacks and airstrikes have escalated as a rapidly-moving government offensive gains momentum, jeopardizing the safety of hundreds of thousands of civilians," said Zeid.
He said that at least 85 civilians, including 21 women and 30 children, have been killed and at least 183 injured in eastern Ghouta since December 31.
The push toward Abu Zuhour came as the opposition's Britain-based Syrian Observatory for Human Rights reported several explosions in the coastal province of Latakia, an Assad stronghold. The Observatory said the blasts were the result of explosions in an arms depot east of Latakia.
State media did not report any blasts in the area.
Russia's Defence Ministry said its forces repelled a series of drone attacks on Saturday, adding that out of the 13 drones involved, seven were shot down and six were forced to land without inflicting any damage.
Russia entered the civil war in 2015 to bolster government forces, helping them to secure a series of victories against the Islamic State group as well as mainstream rebels.
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