Cops circle Oommen Chandy's car following the attack on Sunday evening.
The opposition Left in Kerala has denied that its workers were involved in the attack on Chief Minister Oommen Chandy, who is in a hospital following injuries after stones were pelted at his car yesterday evening.
"It is our belief that Left workers were not involved, but let's wait for a probe," the CPM leader MA Baby told NDTV.
"The attack is unfortunate, but out agitation against the state government in the solar scam will continue," Mr Baby said.
The ruling Congress alliance has rejected the denial, alleging that the attack was pre-planned. "The opposition has crossed all limits in its protests. Kerala's history has not seen such an incident," a senior minister in Mr Chandy's government told NDTV.
It was during a Left demonstration over the solar scam that protesters pelted stones at Mr Chandy at Kannur, where he had gone to attend a couple of engagements including the valedictory of the state police athletic meet.
The protesters, who sneaked into the venue despite heavy security, stoned Mr Chandy's car shattering its glass pane, splinters of which hit his forehead above the right eye. A stone also hit his chest.
21 people have been arrested for the attack, police said.
The solar scam - an alleged con job by a pair of entrepreneurs including a woman named Saritha Nair - has engulfed Mr Chandy for months now with records showing members of his office in frequent touch with the couple.
Ms Nair and her partner, Biju Radhakrishnan, are accused of swindling several people and companies by failing to deliver on solar energy solutions they had promised. They are in jail along with Teny Jopan, who was the chief minister's personal assistant.
Earlier today, the CPM stalwart and opposition leader in Kerala Assembly, VS Achuthanandan, visited Mr Chandy at a hospital in Thiruvananthapuram. Mr Achuthanandan condemned the attack but declined to make any statement to the reporters.