LONDON (AP) Britain's Foreign Office summoned Spain's ambassador on Tuesday to express concern over what it calls an ongoing incursion in Gibraltar's waters, the latest incident in a spat over the disputed U.K. territory.

Tension has grown after Gibraltar built an artificial reef that Spain says hurts its fishermen. Spain retaliated by beefing up border security, creating delays.

Earlier this month, the U.K. complained to Spain after a minor boat collision off Gibraltar.

On Tuesday, Britain's Foreign Office said that despite "repeated diplomatic protests" in recent months, a Spanish research vessel has been carrying out unauthorized surveys in Gibraltar's waters. The vessel undertook "significant surveying activity" for over 20 hours starting on Monday, it added in a statement.

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It strongly condemned the "provocative incursion" and summoned the Spanish ambassador to express the U.K.'s serious concerns the third time the Spanish ambassador has been publicly summoned over Gibraltar issues since the current Spanish government took office in December 2011.

According to the Foreign Office, the acting permanent undersecretary Matthew Rycroft told Spain's ambassador, Federico Trillo, that incursions were unlawful.

Rycroft also raised the issue of long delays at the border between Spain and Gibraltar an issue that has been exacerbating tensions in recent months.

The move came on the day of the British colony's international soccer debut, seen by some as a legitimization of the territory's status. The team played Slovakia to a 0-0 draw in Portugal.