* Second such attack in Dadaab camp this month
* Police car was leading U.N. convoy
* Two private security guards seriously wounded (Adds colour, witness, details)
By Daud Yussuf and Noor Ali
GARISSA, Kenya, Nov 15 (Reuters) - A remote-controlled bomb blew up a police vehicle escorting a U.N. convoy in Kenya's Dadaab refugee camp near the border with Somalia on Tuesday, the second such incident in the camp this month.
A U.N. driver said the blast ripped through the back of the police jeep moments after the column of ten vehicles had left Hagadera, one of three camps in the sprawling complex, wounding two private security guards and two police officers.
Two refugees from the camp were arrested in connection with the attack, police spokesman Eric Kiraithe said in a statement.
Kenya has been plagued by a wave of attacks since it sent hundreds of soldiers into neighbouring Somalia last month to crush the al Qaeda-linked al Shabaab militant group.
"The police car was at the front of the convoy. As we drove out of Hagadera we saw an explosion at the rear end of the landcruiser," said the driver who declined to be named.
"My car was third in the convoy," he said.
Abukar Mohamed, a local bus driver, said the blast took place a few hundred metres from the bus park where he was at the time, and sent people scrambling for shelter.
"I then ran to the site of the blast. The two G4S security guards were seriously wounded, they were bleeding all over. The two policemen had minor injuries," he said.
Witnesses said the attack left a two-metre crater in the sand track.
Dadaab, located about 100 km (60 miles) from the Somali border, was set up in 1991 to house Somalis fleeing violence in their country. The camp's population has swollen to more than 460,000 people this year because of famine in the lawless country.
Two Spanish aid workers were kidnapped from Dadaab, the world's largest refugee camp, and taken into Somalia last month, victims of a rash of abductions of Westerners in Kenya that spurred the country to deploy forces across the border.
Banditry is common around the camp but targeted bomb attacks are rare.
Tuesday's attack underscored the mounting threats facing aid workers and refugees in the camp.
The U.N.'s refugee agency, UNHCR, has already cut back its aid operations to essential services, namely distribution of food, water and health care in the camps where cholera has broken out.
"This kind of act will not deter the police force from performing its duty, of offering security and ensuring our country is protected against any evil characters, bandits or militias from Somalia," Leo Nyongesa, the police commander of North Eastern province, told Reuters.
Kenya, the region's biggest economy, is the latest country in a string of foreign powers to try and stabilise the Horn of Africa country that has been mired in violence for two decades.
Analysts warn Kenya's incursion risks dragging it into a broader regional conflict.
Somalia's al Shabaab militants have vowed to bring the "flames of war" across the frontier in retaliation. Security experts have also voiced concerns the rebels would increasingly turn to softer targets, such as tourists and aid workers.
Another Kenyan police truck escorting U.N. vehicles hit a landmine in the same area earlier this month, but the explosive failed to detonate. (Additional reporting and writing by Richard Lough in Nairobi; editing by Matthew Jones)