NAIROBI, March 23 (Reuters) - Kenya plans to build a new road, more border crossings and barriers on its 700 km (420 mile) border with Somalia in an attempt to thwart attacks from the Islamist militant group al Shabaab, the interior ministry said on Monday.

Kenya is under heavy pressure to improve security after numerous militant attacks that have killed well over 200 people since 2013, mostly in the border counties of Mandera and Lamu.

The al Qaeda-linked al Shabaab group has claimed responsibility for much of the bloodshed and has vowed revenge against Kenya for contributing troops to an African Union force battling the militants in Somalia.

"The idea is to ensure that there are clear border entry points," said Mwenda Njoka, a spokesman for Interior Secretary Joseph Nkaissery.

"It's not that you're going to put up a 700 km wall."

Njoka said authorities had sent surveyors to the crime-ridden border region, which is awash with bandits and gunmen and includes hundreds of kilometres of dense forest and marshes.

Njoka said the project should begin this financial year but could not say how much it would cost, when it would be completed or how many additional patrol guards would be deployed. It was also not immediately clear whether the planned new road would run the full length of the border with Somalia.

Critics on social media were quick to mock the plan, saying the government would do better to focus on tackling corruption. Analysts say it is possible to purchase a Kenyan passport for $100, while those caught up in police sweeps targeting suspected terrorists pay bribes to be released from jail.

Nkaissery was appointed interior minister last December as part of a security shake-up following two attacks in Mandera, northeast Kenya.

Those raids angered many Kenyans and prompted President Uhuru Kenyatta to replace his top security officials and push through a new law with sweeping counter-terrorism powers.

This month, in the most recent strike claimed by al Shabaab, gunmen attacked the convoy of Mandera governor Ali Roba, killing four soldiers. (Reporting by Edith Honan; Editing by James Macharia and Gareth Jones)