China tightens security in Beijing
China has deployed armed police patrol vehicles in Beijing after three attacks at transport hubs around the country.
The 150 vehicles are tasked with "countering street terrorism and fighting severe violence", state-run Xinhua news agency said.
Petrol purchases would also be tightened, with buyers required to register with police, reports said.
The move follows station attacks in Kunming, Urumqi and Guangzhou, and comes before the Tiananmen anniversary.
Xinhua said the armed police patrols would be stationed at major road junctions and manned by at least nine police officers and other assistants.
They would cover an area of 3km (1.8 miles) and would be required to respond within three minutes, Xinhua added.
Meanwhile, those buying petrol would have to explain their intentions in a move that aimed to prevent the use of gasoline "to create disturbances", People's Daily newspaper said.
Uighurs and Xinjiang
- Uighurs are ethnically Turkic Muslims
- They make up about 45% of the region's population; 40% are Han Chinese
- China re-established control in 1949 after crushing short-lived state of East Turkestan
- Since then, there has been large-scale immigration of Han Chinese
- Uighurs fear erosion of traditional culture
The security upgrade comes amid heightened concern over security after the three station attacks.
March's group knife attack in Kunming left 29 people dead and more than 100 wounded. A similar attack in Urumqi in April left three people dead and almost 80 injured.
Chinese authorities have blamed both attacks on separatists from the Muslim Uighur minority group, which lives in Xinjiang.
It is not yet clear what sparked an attack last week at Guangzhou station in which six people were hurt. One man is reported to be in custody.
In October 2013, meanwhile, five people died and dozens were injured after a car drove into a crowd near Tiananmen Square and burst into flames.
Officials said three of those who died - the occupants of the car - came from the Uighur minority group.
The Uighurs, who are ethnically Turkic Muslims, say that large-scale Han Chinese immigration into Xinjiang has eroded their traditional culture and accuse Beijing of oppressive control.
There are sporadic violent incidents - in 2009, bloody ethnic riots in Urumqi left about 200 people dead.
Chinese authorities, meanwhile, say they have invested heavily in the region to improve people's lives.
The boost in security in Beijing also comes three weeks ahead of the 25th anniversary of the crackdown on anti-government protesters at Tiananmen Square.
Several well-known activists, including journalist Gao Yu, have been detained ahead of the anniversary.