The Syrian opposition says rebel forces have killed 28 government soldiers during attacks on three army checkpoints as the violence in Syria escalates.

The Britain-based Syrian Observatory for Human Rights confirmed that the attacks occurred Thursday in the northern province of Idlib, near the Turkish border. It said five rebels were killed in the skirmishes.

There was no comment from the Syrian government.

In neighboring Turkey, a car full of explosives blew up in the port town of Iskenderun near the Syrian border. Four people were killed. It was not immediately clear if the blast was linked to the Kurdish militants or the Syrian conflict.

Turkey is home to more than 100,000 Syrian refugees and opposition leaders who live in camps along the border.

The Syrian conflict is entering its 20th month and has caused the deaths of an estimated 36,000 people. Hundreds of people were killed in the past week as the government has stepped up airstrikes against rebel-controlled areas.

U.S. Secretary of State Hillary Clinton Wednesday addressed concerns that Islamic extremists who have fought alongside the rebels are radicalizing the opposition.

She said Washington hopes that Syrian opposition talks next week in Doha will produce a new rebel leadership that represents those fighting and dying in the country. She said the Syrian National Council, composed mainly of exiles, can no longer be viewed as the leader of the opposition, but it can still play a role.