At least four people have died and dozens were injured following a series of coordinated bomb attacks across tourist towns in Thailand.

Four bombs exploded in the resort town of Hua Hin, and several blasts were reported in Phuket. Others explosions also occurred in Surat Thani, Phang Nga and Trang. The bombs were detonated using mobile phone timers in each attack.

Witnesses at one site in Hua Hin said a bomb had been hidden in plant pots on a street filled with restaurants and bars.

Sky News also reports that investigators found ball-bearings at the scene which they believe were put in the bombs to cause maximum injury.

Foreign nationals were among the 35 injured.

The British embassy in Thailand has updated its travel advice urging tourists to exercise “extreme caution” and to avoid public places.

“We are in close contact with local authorities and urgently seeking more information. You should exercise extreme caution, avoid public places, and follow the advice of local authorities.”

Police have ruled out international terrorism and said links to the southern insurgency were unclear, the BBC reports.

The attacks seems to have particularly focused on tourist areas, with the Hua Hin explosions on Thursday night striking a bar area popular with tourists, and foreigners were among those injured.

The choice of Hua Hin as a target is also symbolic, the BBC noted. It is recognised as being a royal city and the king’s favoured residence outside Bangkok.

Police have reportedly ruled out international terrorism and said they had detained some suspects. Security is understood to have been tightened in the tourist areas and at airports in the south of the country. Brant Smith, from Canberra in Australia and on holiday in Hua Hin, told the BBC that people in the resort were “rattled” and that there was tight security around his hotel.