The Syrian government has decided to allow permanent United Nations aid teams in four cities for the first time since conflict erupted in the country last year.

The humanitarian breakthrough came as President Bashar al-Assad's government decided to expel 17 diplomats from Turkey and a number of Western nations, a response to a similar decision by those countries to expel their Syrian envoys.

Meanwhile, violence continues throughout the country, and activist video shows troops outside Homs using heavy mortars to bombard the city.

Al Jazeera's Dominic Kane reports.