New Delhi: Senior Congress leader Shashi Tharoor on Monday said he has declined CPM's invitation to its party seminar in Kerala after discussing the issue with AICC president Sonia Gandhi.

The Left party had invited Thiruvananthapuram MP, Tharoor, and former Union minister Thomas to attend seminars ahead of its 23rd Party Congress scheduled to be held at Kannur in the state from April 6-10.

Seemingly upset over criticism directed at him by some state Congress leaders, Tharoor said a similar invitation was extended a month ago for a seminar on the sidelines of the CPM State Party Conference and on that occasion also, he consulted the AICC president and a suitable decision was taken without any media controversy.

"A similar procedure could easily have been followed this time also. I regret that some preferred the unseemly public airing of internal differences, thereby creating a needless controversy in a matter in which AICC's view was binding. I hope wisdom will prevail in future," he said in a statement.

Tharoor said he has discussed with the AICC president, the matter of his participation in the seminar on Centre-state relations on the sidelines of the CPM National Party Congress.

"I had welcomed the invitation on the following grounds -- The event is a national one and the highest forum of the CPM, organised by its Central Committee, and formulates its national policy. Nationally we have a cooperative relationship with the CPM; The topic for the seminar does not involve any matter of sensitivity in Kerala but is on 'Centre-state relations', where there is no real difference of opinion between our  parties; The event sets a fine example of intellectual exchange on policy issues among 'anti-BJP opposition parties', which should in principle be encouraged," he said.

"I respect her views on this matter and have conveyed to the organizers my inability to participate," Tharoor added.

The Lok Sabha MP said broader questions of the Congress' relations with the CPM at the national level, the specific topic of Centre-state relations, and the manner in which invitations from other political parties should be handled, remain to be addressed separately.

Earlier, Manorama News reported that the Congress high command had shot down Tharoor's request seeking permission to attend rival CPM's seminar.

According to reports, Congress chief Sonia Gandhi had instructed Tharoor to stand by the Kerala Pradesh Congress Committee decision (KPCC).

The development came amid strong protests from fellow party workers in Kerala.

Earlier, KPCC chief K Sudhakaran had urged his colleagues to stay away from CPM forums.

He had said that it was "unacceptable to the party workers to see their leaders attend the forums of rival parties".

Sudhakaran had warned that strict action would be taken if any leaders violated the party stance.

However, Tharoor contested this by saying that the CPM Party Congress was a national event and that it was not inappropriate to voice opinions by participating in it.

He said dialogues were essential between members of different political parties in a democracy.

It was after this that the high command involved in the matter.

The high command's denial of permission to Tharoor also comes at a time when Congress-led United Democratic Front is locked in battle with the CPM-led Left government on the SilverLine railway project.

Earlier, Tharoor had also shown a positive leaning towards the implementation of this project despite Congress deeming the whole CPM endeavour a misadventure, one certain to plunge the state into further ecological and economic turmoil.

The 529.45 km long SilverLine railway project is expected to reduce the journey time from Thiruvananthapuram to Kasaragod from 12 hours to just 4 hours.

According to a Detailed Project Report (DPR) published on January 15, the estimated cost of the SilverLine project is Rs 63,941 crores. It is expected to be complete only by 2025.

However, the Centre is yet to approve the project.

Shashi Tharoor is an MP from Kerala's capital, Thiruvananthapuram.

The CPM or Communist Party of India Marxist is the ruling government in Kerala and Congress' arch-rivals in the state.

The CPM had invited a host of senior Congress leaders including Tharoor, Ramesh Chennithala and KV Thomas for seminars as part of its 23rd Party Congress.

It is scheduled to be held from April 6 to 10 in Kannur.