New clashes erupted Tuesday in an intensifying battle for control over Aleppo's international airport and nearby military bases in Syria's north, activists said.

Rebels have tried for weeks to capture Aleppo's international airport and nearby air bases as part of their campaign to erode the regime's air supremacy in the 2-year-old conflict that the United Nations says has claimed more than 70,000 lives.

Rebels have made significant strategic advances in the north in the past months, capturing military bases, two dams on the Euphrates river and the city of Raqqa in the northwest _ the first urban area to fall into opposition hands since the uprising against Assad's regime began in March 2011.

The rebels also control large swathes of land outside of Aleppo. The battle for the city itself, Syria's main commercial hub, is locked in a stalemate. Rebels pushed into the city in July and captured several neighborhoods and it has been a major battleground in the civil war ever since.

The army still holds large parts of Aleppo and maintains control over the airport, the country's second largest. Crucially, Syria's air space is firmly controlled by the regime in Damascus, which uses its warplanes to regularly bomb rebel strongholds.

The Syrian Observatory for Human Rights said clashes erupted anew on Tuesday around the airport and rebels also intensified their assault on the Nairab and Mannagh air bases near the strategic facility, which has not been handling fights for weeks because of the fighting.

There were also intense clashes at another nearby airfield known as Kweiras, according to the Observatory, a Britain-based anti-regime group that relies on a network of activists on the ground.

Fighting also raged for a second day in the central city of Homs as rebels tried to take back the poor neighborhood of Baba Amr, which they lost to President Bashar Assad's troops a year ago.

Last year, government forces besieged Baba Amr for a month before rebel forces withdrew and the government seized control on March 1. Hundreds of people were killed in the siege.

On Sunday, rebels pushed back into Baba Amr and Syrian forces responded on Monday by firing heavy machine guns into the neighborhood, sending residents fleeing.

In Geneva, The U.N. food agency said the renewed violence in Baba Amr has forced at least 3,000 families to leave their homes in the contested area.

The World Food Program said in a statement that more than 1,000 of the displaced families have taken refuge in six schools in Homs and some 2,000 families are staying in public shelters or with relatives in different parts of the governorate.

It was unclear how much of the neighborhood rebels had seized or continued to hold after the latest fighting in the area.

In Kiev, Ukraine's Foreign Ministry confirmed that a Ukrainian journalist who was kidnapped in Syria is free after being held by rebels for more than 150 days.

Ministry spokesman Yevhen Perebiynis said the reporter, Ankhar Kochneva, was expected to contact the Ukrainian embassy in Damascus later in the day.

Kochneva, who has written for Syrian and Russian newspapers, was kidnapped in western Syria on Oct. 9. Russian media reported she had been held by members of the Free Syrian Army opposition group. Perebiynis said he had no further information on her.

The Russian newspaper Komsomolskaya Pravda quoted Kochneva as saying she walked away from the house where she was held, skirted a rebel guard post and then walked about 15 kilometers (9 miles) through fields until finding a villager who helped her.

According to the newspaper, Kochneva said she was abducted near the city of Homs while riding in a taxi to Damascus.

The abductors released a video in which Kochneva said she was working as a Russian agent, but the newspaper quoted her as saying the recording was made under duress.

Russia is a staunch ally of Damascus, supplying the Assad regime with weapons and shielding his government from tougher U.N. sanctions.

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Associated Press writers Anna Melnichuk in Kiev, Jim Heintz in Moscow and John Heilprin in Geneva contributed to this report.