Article 22.2 of the Vienna Convention on Diplomatic Relations seems to support what the Americans are complaining about:
The receiving State is under a special duty to take all appropriate steps to protect the premises of the mission against any intrusion or damage and to prevent any disturbance of the peace of the mission or impairment of its dignity.
However, Article 41.1 is worth checking out:
Without prejudice to their privileges and immunities, it is the duty of all persons enjoying such privileges and immunities to respect the laws and regulations of the receiving State. They also have a duty not to interfere in the internal affairs of that State.
There have been other threads about venezuela recently. In one of them I pointed out that Oil exports to the US were 1.6 million barrels in 1991. This figure fell to 1.3 million by 2003 and is estimated at being around 1 million last year (and still falling).
Venezuela was onr of the founding members of OPEC and petroleum accounts for something like 80% of its export income and about 33% of the Gross Domestic Product. That puts it in the big league insofar as the US is concerned. Any disturbance from this nation in terms of supply is economically threating to the US - hence the interest in 'liberating' it from unwelcome tendencies.
And conversley the reason for certain attitudes and responses from Venezuela - in all a situation of poo type scale waiting to be dropped!
If this was the only incident it wouldnt be that big a deal, but its the 3d in a little over a week. The Venezuelan Ambassador was summoned to the State Department and was told that if there are any more repeats the Venezuelan embassy staff would be restricted to their embassy.