The Spanish foreign ministry has summoned the Venezuelan ambassador to once again protest comments by Venezuela's president against Spanish Prime Minister Mariano Rajoy.

The ministry said in a statement it had expressed to Ambassador Mario Isea on Monday the government's "dislike and rejection of the unacceptable insults made once again" by President Nicolas Maduro.

Maduro on Saturday called Rajoy a "hitman" in comments on the European Union's handling of the Greek crisis.

The ambassador was summoned in April for similar reasons and Spain later temporarily recalled its ambassador to Venezuela.

The ministry said Spain wished for constructive relations with Venezuela base on mutual respect, regardless of their differences.