* EU, US, Arab League impose more sanctions on Syria
* Six civilians killed in army sweep of town -- rights group
* U.N. official says at least 4,000 killed since March (Adds sanctions widened, estimated death tolls, IEDs defused)
BEIRUT, Dec 1 (Reuters) - The United States, European Union and Arab League blacklisted Syrian VIPs and companies on Thursday to force an end to the military crackdown on protesters challenging the rule of President Bashar al-Assad.
Bloodshed continued in Syria in what one United Nations official said was now a "civil war" that has cost at least 4,000 lives since March.
Six people were killed and five critically wounded during an army sweep into the restive town of al-Trimsa in Hama province, a hotbed of anti-Assad sentiment, the Syrian Observatory for Human Rights said. At least four were killed in other incidents as troops backed by tanks rounded up suspects by the score.
The Observatory, which keeps an hour-by-hour account of violent incidents, says 4,530 people have died in eight months of unrest, 1,244 of them from the security forces.
EU foreign ministers in Brussels agreed to impose new sanctions on Syria's oil and financial sectors, and added 11 entities and 12 people to its list of those targeted by asset freezes and travel bans.
The U.S. Treasury Department blacklisted two more Syrian officials and two financial institutions.
An Arab League committee convening in Cairo listed 17 Syrian VIPs banned from travel to Arab states, including Assad's brother Maher who commands the military's elite Republican Guard and is Syria's second most powerful man.
President Assad was not named in the travel blacklist.
Kuwait joined the list of Gulf countries advising nationals to leave Syria for safety reasons.
The crisis erupted in March with street protests inspired by anti-authoritarian revolts elsewhere in the Arab world. But in reaction to Assad's iron fist policy, army units have defected with their weapons to fight loyalist troops.
The state news agency SANA said border guards killed and arrested several people from "armed terrorist groups who infiltrated over the border (from Turkey) and attacked an observation point" in the northwestern district of Idlib. A border guard died during "long clashes", SANA reported.
It said army experts had defused two explosive devices planted in a country road near the city of Homs.
U.N. High Commissioner for Human Rights Navi Pillay said she had told the U.N. Security Council in August "it is going to be a civil war".
"At the moment that is how I am characterising it. We are placing the (death toll) at 4,000, that is conservative, the reliable information coming to us is that it is much more than that," Pillay told a news conference in Geneva.
Western and Arab governments are demanding that Assad withdraw forces from restive cities, free prisoners and start talks with the opposition on greater political freedoms. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ TAKE A LOOK: Unrest in Syria ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^>
The 27-member EU was expected on Friday to name names and cite firms on its expanded sanctions list. The Syrian state oil company General Petroleum Corporation (GPC) was among companies deemed to be supporting what the EU calls the Assad regime, diplomats said.
Oil majors such as Royal Dutch Shell and France's Total could see their Syrian ventures grind to a halt as the GPC joins the roster of sanctioned companies, diplomatic sources told Reuters.
Already blacklisted by the U.S. Office of Foreign Assets Control, GPC is responsible for supervising joint venture companies in Syria. Royal Dutch Shell and China National Petroleum Corporation are both partners of GPC through the Al-Furat joint venture.
Some diplomatic sources said the blacklisting would likely make it hard for European oil firms to keep operating in Syria. Syria contributes less than 1 percent to daily world oil output but oil brings in a big chunk of Syrian government earnings.
Turkey, Syria's biggest trade partner, suspended all financial credit dealings with Damascus on Wednesday and froze its assets, joining the Arab League in isolating Assad.
Western leaders show no enthusiasm for NATO intervention in Syria of the sort that helped rebels topple Libyan dictator Muammar Gaddafi. Syria has friends in Tehran and Moscow, and Assad still has support at home.
But Turkey, a NATO member with a 900-km (560-km) long border with Syria, says it does not want intervention in its fellow Muslim state. It has raised the possibility of establishing a buffer zone should there be a mass exodus of Syrians. (Additional reporting by Omar Fahmy in Cairo, David Brunnstrom and Justyna Pawlak in Brussels; Glenn Somerville in Washington; Stephane Nebehay in Geneva; Erika Solomon in Beirut; editing by Mark Heinrich)